THE  ANALYSIS  OF  COPPER 


McGraw-Hill  BookGompany 


Electrical  World         The  Engineering  and  Mining  Journal 
Engineering  Record  Engineering  News 

Railway  Age  Gazette  American  Machinist 

Signal  E,ngin<?0r  American  Engineer 

Electric  Railway  Journal  Coal  Age 

Metallurgical  and  Chemical  Engineering  Power 


THE 

ANALYSIS   OF   COPPEE 


ITS  ORES  AND  ALLOYS 


BY 

GEORGE  L.  HEATH 

CHIEF   CHEMIST,    CALUMET  &   HECLA  SMELTING   WORKS 

MEMBER,    AMER.   INSTITUTE   OF  MINING  ENGINEERS 
AMER.   CHEMICAL  SOCIETY,   SOCIETY  FOR  TESTING   MATERIALS 


FIRST  EDITION 


McGRAW-HILL  BOOK  COMPANY,  INC. 

239  WEST  39TH  STREET,  NEW  YORK 


LONDON:  HILL  PUBLISHING  CO.,  LTD. 

6  &  8  BOUVERIE  ST.,  E.  C. 

1916 


COPYRIGHT,     IQl6,    BY    THE 
MCGRAW-HILL    BOOK    COMPANY,    INC. 


; 


*  PREFACE 

THIS  volume  constitutes  the  first  connected  representative 
account  of  the  principal  methods  employed  by  the  largest  re- 
fineries, foundries,  and  custom  sampling  works  for  the  control  of 
operations  and  valuation  of  material,  following  the  logical  sequence 
from  the  ore  in  the  mine  to  the  finished  metallic  product.  The 
book  is  accordingly  intended,  primarily,  for  the  technical  chemist 
and  advanced  student. 

As  there  is  considerable  similarity  in  methods  of  assaying 
adopted  at  reduction  works  situated  west  of  the  Mississippi  river 
in  the  United  States,  the  methods  reported  by  the  largest  con- 
cerns will  be  designated,  by  request,  as  "  Western  methods." 

Comparatively  recent  papers  by  engineers  and  chemists  have 
emphasized  the  fact  that  the  correct  sampling  is  an  absolute 
necessity.  In  consequence,  a  special  feature  has  been  made  of 
this  subject,  although  it  has  been  neglected  in  other  chemical 
books.  A  scheme  for  the  sampling  of  coal  on  a  large  scale  has 
been  included,  but  the  analytical  work  has  been  omitted  because 
a  book  on  this  special  subject  has  recently  been  published. 

The  author  takes  pleasure  in  giving  credit  where  it  is  due  by 
recording  the  names  of  those  who  have  shown  an  interest  in 
making  the  account  representative  of  the  latest  practice  of  the 
large  producers  and  consumers  of  copper,  or  have  contributed 
material  which  has  been  included  in  the  text.  Among  these  are 
the  late  J-.  B.  Cooper  and  M.  B.  Patch,  formerly  Supts.  of  C.  &  H. 
refineries ;  E.  P.  Mathewson,  Mgr.,  and  Chief  Chemist,  Anaconda 
Co.;  Dr.  E.  Keller,  Perth  Amboy,  N.  J.;  W.  H.  Bassett,  Tech- 
nical Supt.,  Alden  Merrill,  Chemist,  American  Brass  Co.;  C.  H. 
Benedict,  Metallurgist,  C.  &  H.  Mining  Co.;  J.  R.  Agnew,  Supt. 
and  J.  W.  Rawlins,  Chemist,  Canadian  Copper  Co.;  A.  Alexander. 
Mgr.,  F.  Andrews,  Chief  Chemist,  Raritan  Copper  Works ;  A.  M. 
Smoot  (Ledoux  &  Co.),  New  York;  L.  Addicks,  Douglas,  Ariz. 
F.  D.  Greenwood,  Chief  Chemist,  U.  S.  Metals  Refining  Co. 
J.  Klein,  Chemist,  Buffalo  Rolling  Mill ;  R.  Franke,  Director,  anc 
H.  Koch,  Chief  Chemical  Inspector,  Mansfeld  Works,  Eisleben 


344726 


vi  PREFACE 

Dr.  Toisten,  Chemist  of  the  Mansfeld  Brass  Works,  Hettstedt, 
Germany ;  Prof.  R.  H.  Richards  and  Prof.  C.  R.  Hayward,  Boston. 
Valuable  aid  has  also  been  received  from  assistants  in  the  modifi- 
cation of  two  or  three  methods,  and  from  the  papers  of  F.  P. 
Dewey,  W.  C.  Ferguson,  F.  G.  Hawley,  G.  C.  Stone,  and  others. 

June,  1916  GEORGE  L.  HEATH 


CONTENTS 


PAGE 

PREFACE »  ^v  . v 

CHAPTER  PART  I 

I.    INTRODUCTION 1 

II.    SAMPLING  AND  CRUSHING 14 

III.  REAGENTS  AND  STANDARD  SOLUTIONS 37 

IV.  THE  ASSAY  OF  COPPER  IN  ORES  AND  FURNACE  PRODUCTS  .    .  51 
V.    ANALYSIS  OF  ORES,  SLAGS,  MATTE,  AND  FLUE  DUST     ....  69 

VI.    SPECIAL  ELEMENTS  IN  ORES,  SLAGS,  AND  MATTE 83 

VII.    SPECIAL  DETERMINATIONS  IN  ORES,  SLAGS,  AND  MATTE  CON- 
CLUDED—  FURNACE  REFRACTORIES 101 

VIII.    FIRE  ASSAYING  FOR  COPPER,  LEAD,  SILVER,  GOLD  AND  PLATI- 
NUM IN  ORES  AND  FURNACE  BY-PRODUCTS 125 

PART  II 

IX.    WORK  OF  THE  ELECTROLYTIC  REFINERY 143 

X.    THE  ELECTROLYTIC  REFINERY,  CONCLUDED 165 

PART  III 

XI.    THE  ELECTROLYTIC  ASSAY  OF  REFINED  COPPER 183 

XII.    THE  DETERMINATION  OF  FOREIGN  ELEMENTS  IN  COPPER    .   .  191 

XIII.  SPECIAL  METHODS  FOR  FOREIGN  METALS  IN  COPPER    ....  214 

PART  IV 

XIV.  ANALYSIS  OF  THE  PRINCIPAL  COMMERCIAL  ALLOYS  OF  COPPER  236 

PART  V 

XV.    METALLOGRAPHY  OF  COPPER  AND  BRASS 259 

XVI.    THE  ELECTRICAL  RESISTIVITY  OF  COPPER 272 

• 

INDEX  .  281 


vn 


ANALYSIS  J3F    COPPER 

PART   I 

CHAPTER  I 
INTRODUCTION 

1.  Although  the  principal  title  of  this  book  is  the  "  Analy- 
sis of  Copper/'  the  treatment  of  the  subject  is  more  compre- 
hensive and  includes  the  analysis  of  copper  bearing  minerals, 
mattes,  slags,  and  other  metallurgical  products.  In  this  connec- 
tion methods  are  given  for  the  quantitative  determination  of 
most  of  the  common  metallic  elements  and  for  some  of  the  rarer 
ones.  The  chapters  are  divided  into  five  groups,  the  arrange- 
ment of  the  subject  matter  following  the  progress  of  the 
copper  from -the  mine  to  the  finished  product.  The  standard 
methods  used  in  western  ore-reduction  works  are  designated  by 
request  as  "  Western  methods,"  and  when  two  or  more  methods 
are  included  for  the  estimation  of  a  single  constituent,  the  first 
is  to  be  preferred  unless  the  field  of  each  is  specified.  All  are 
standard  methods  in  use  at  some  one  of  the  larger  plants  but 
the  operator  without  special  experience  is  advised  to  select  the 
one  prescribed  for  the  particular  material  treated,  and  neither  to 
omit  any  steps  in  a  process  nor  to  use  a  limited  method  outside 
of  its  prescribed  field,  except  after  careful  experiment. 

No  attempt  is  made  to  give  a  complete  list  of  apparatus  used 
in  metallurgical  analysis  but  a  few  special  improvements  which 
have  been  adopted  in  large  copper  laboratories  to  facilitate 
rapid  work  are  described.  All  apparatus  should  be  suited  to 
the  character  of  the  work,  whether  it  be  ore-assaying  or  the 
delicate  estimation  of  traces  of  impurities  in  refined  metal,  an 
operation  in  which  results  are  calculated  to  a  ten-thousandth  of 
one  per  cent,  or  one  more  decimal  place  than  is  usual  in  report- 
ing tests  of  iron  and  steel.  To  permit  this  degree  of  accuracy 
in  the  examination  of  refined  copper,  the  bulk  of  final  solutions 
and  the  size  of  filter  papers  and  containers  should  be  kept  as  small 
as  possible  without  undue  sacrifice  of  speed. 


>-;  *•«* 

>*"    f 


ANALYSIS  OF  COPPER 


SPECIAL    EQUIPMENT 

2.  Office   Records.  —  Large  works  keep  a  systematic  record 
of  all  tests  except  for  those  of  temporary  character.     A  serial 
number  is   given  to  every  sample  that  comes  to    the    labora- 
tory, and  printed  cards  or  tickets  are  provided  upon  which  are 
entered  all  the  data  of  weights,  sampling,  and  analysis.     These 
records  are  subsequently  bound,  catalogued,  and  filed  away  for 
ready  reference.     A  few  plants  have  adopted  a  system  of  5  x  8 
inch  tabbed  cards  which  are  filed  in  cases,  each  drawer  holding 
1000   cards.     The  U.  S.   Metals  Refining  Co.   use  a  triplicate 
series  of  tickets,  on  which  the  descriptions  are  entered  by  a  clerk 
to  relieve  the  chemists.     The  assay  slips  are  printed  in  three 
colors,  white,  red,  and  yellow,  with  carbon  papers  between  them. 
The  white   slip   is  filed  eventually  in  the  clerk's  office,  the  red 
slip  is  sent  to  the  laboratory  with  the  sample,  and  the  yellow  one 
to  the  assay  department.     After  the  chemist  in  charge  has  checked 
the  work  and  signed  the  assay  certificate  filled  in  by  the  clerk, 
the  yellow  and  red  slips  are  filed  in  the  laboratory. 

The  work  of  the  Mansfeld  Smelter  in  Germany  is  of  a  peculiar 
nature.  The  ore  deposits  are  partly  surface  slates  and  partly 
true  ores  which  contain  a  refractory  mineral  "typolite."  In 
addition  to  daily  reports,  the  completeness  of  German  system 
requires  that  the  chief  chemist  shall  furnish  a  monthly  thirty- 
page  report  of  all  the  work  of  the  month,  including  the  ore 
and  metal  returns  of  mines,  electrolytic  refinery,  and  brass 
works. 

3.  Assay  Furnaces  of  portable  type  are  a  necessity  in  remote 
places.     The  best  of  coal  or  gas  fired  muffle  and  pot  furnaces 
are  the  rule  in  modern  plants.     A  plan  of  a  good  pot  furnace, 
adapted   to  either  native  copper  or  gold  ores,  is  inserted.     The 
depth  of  the  furnace  from  cover  to  grate  is  61  cm.  and  the  grate 
area  32  x  46  cm.     The  ash-pit   door   is   made  with    an   extra 
weight,  so  that  a  blast  of  air  may  be  admitted  under  the  grate 
through  a  pipe  6.3  cm.  in  diameter.     The  air  may  be  furnished 
by  the  smallest  Roots'  blower,  belted  to  a  shaft  in  the  sampling 
room  and  driven  by  a  small  five-horse  power  electric  motor. 

4.  The  Furnace  Accessories,  devised  by  Dr.  E.  Keller,  are  of 
assistance  in  rapid  work,  especially  on  bullion.1     A  cupel  charger 

1  Trans.  A.I.M.  E.  36  (1906),  3. 


INTRODUCTION 


permits  48  cupels  to  be  placed,  or  withdrawn,  as  a  unit.  The 
front  row  of  assays  are  blanks,  .the  other  40  being  charged  with 
the  lead  buttons.  Other  devices  are  parting  baths  with  holders, 
multiple  scorifier  tongs,  a  stirring  machine  to  be  used  with 


Cross   Section  ErF 


Cross  Section   C~B 


Common  Brick 


Cross  Section  GrH 

Fig.  1.  —  Assay  Furnace. 

beakers,  and  a  mechanical  filtration  apparatus  in  which  20  silver 
assays,  contained  in  750  c.c.  beakers,  may  be  filtered  simultane- 
ously. Although  riffles  of  correct  design  are  easily  purchased, 
they  are  quickly  and  cheaply  made.  Haultain  has  described 
their  manufacture.1 

1  Eng.  and  Min.  Jour.  73  (1907),  232. 


ANALYSIS  OF  COPPER 


APPARATUS  —  STANDARD    FLASKS    AND    ALIQUOTING 
PIPETTES 

5.   Copper  Flasks,  as  they  are  called,  and  automatic   "  wash- 
out" pipettes  are  used  in  the  electrolytic  assay  of  crude  copper. 
Water-jacketed   "  deli  very    pipettes"    have    been    described    by 
W.   C.   Ferguson    of    the  Nichols  Co.1     A.    M. 
Smoot    gives    the    following    directions    for    his 
simple    " wash-out"    pipette,   to  which  the  liter 
"copper  flasks"   are  adjusted  in  mutual  agree- 
ment. 

"In  assaying  inhomogeneous  materials,  such 
as  blister  or  converter  borings,  which  consist 
of  roughly  pulverized  coarse  and  fine  parts 
differing  from  each  other  in  composition,  it  is 
necessary  to  weigh  out  a  charge  large 
enough  to  cover  the  variations.  In  some 


Fig.  2.  — Liter 
Flask  for  Copper 

Assay. 


cases,  a  preliminary  separation  of  the 


coarse  and  fine  parts  of  the  whole 
sample  is  essential.  The  charge  for 
assay  is  then  formed  by  taking  proportionate  weights 
of  each  part.  In  any  case,  the  sample  to  be  weighed 
for  assay  will  be  larger  than  can  be  conveniently  elec- 
trolyzed  directly. 

"Aliquoting  apparatus  is  therefore  necessary,  but 
the  ordinary  flask  and  hand  pipette  are  not  sufficiently 
accurate.  Measurements  within  an  error  of  one  or  two 
hundredths  of  a  per  cent  are  essential  in  dividing  strong 
solutions  of  material  rich  in  copper.  A  convenient  liter 
flask  is  shown  in  Fig.  2  and  the  pipette  in  Fig.  3. 

"  The  flask  has  an  enlarged  neck  which  not  only 
facilitates  the  introduction  of  the  sample  and  reagents, 
but  also  renders  the  mixing  of  the  solutions  much  easier 
when  the  volume  is  made  up  to  the  mark.  The  necks 
of  these  flasks  below  the  enlargement  should  be  narrow, 
so  that  the  meniscus  may  be  clearly  defined  against  the  mark. 

"Mechanical  pipettes  2  with  an  automatic  zero  point  may  also 
be  made  to  deliver  the  required  volume,  but  in  order  to  retain  the 
required   accuracy,   such   pipettes  must  be  rigidly  mounted  to 
i  J.  Ind.  and  Eng.  Chem.  2  (1910),  187.  2  Ibid. 


Fig.  3.— 
Pipette. 


INTRODUCTION  5 

prevent  vibration,  and  must  be  kept  scrupulously  clean,  since  a 
trace  of  adhering  dirt  or  grease  will  make  a  difference  in  the 
volume  actually  delivered.  Such  delivery  pipettes  are  usually 
provided  with  a  lower  stop  cock^land  the  slightest  variation  from 
the  perpendicular  in  opening  it  will  retard  the  flow  of  liquid,  caus- 
ing a  slight  error.  Each  form  of  pipette  has  its  advocates. 

"Hand  Pipettes  may  be  used  if  carefully  compared  and  con- 
structed to  hold  instead  of  deliver  an  aliquot  part  of  the  contents 
of  the  flasks,  and  if  the  pipette  is  subsequently  washed  out." 
The  Smoot  pipette  (Fig.  3)  has  a  stop  cock  which  itself  serves  as 
an  automatic  zero  point.  When  the  pipette  is  full,  it  holds  an 
exact  fraction  of  the  contents  of  the  liter  flask  from  the  bottom 
of  the  stop  cock  to  the  end  of  delivery  tube.  On  turning  the 
valve  through  an  angle  of  45°,  air  is  admitted  through  the  funnel, 
allowing  the  contents  to  discharge;  the  pipette  is  then  washed 
with  three  successive  changes  of  water  of  10  c.c.  each,  introduced 
through  the  funnel.  The  wash  water  spreads  over  the  inner 
surface,  removing  every  trace  of  reagent.  The  pipette  is  filled 
from  the  bottom  and  is  worked  automatically  by  a  filter  pump. 
The  mounting  and  connection  are  shown  in  Chapter  X  under  the 
title,  "  Determination  of  copper  by  electrolysis." 

ELECTRICAL    DATA 

6.  Normal  Current  Density,  in  the  electrolytic  deposition  of 
metals,  is  stated  as  "amperes  per  square  decimeter"  (100  sq.  cm.) 
of  immersed  cathode  surface,  counting  both  sides  of  the  plate 
upon  which  the  deposit  is  made. 

7.  Electrical  power  for  the  determinations  by  electrolysis  is 
usually  delivered  as  a  direct  dynamo  current  of  100-115  volts 
potential.     If  the  current  is  only  available  by  day,  or  is  alternat- 
ing, it  is  better  to  install  a  small  motor-generator  set  or  charge 
storage  cells  to  deliver  a  current  at  6  to  10  volts  tension  than  to 
bother   with   inferior   primary   batteries.     Accumulators   with  a 
capacity  of  10  amperes  and  a  voltage  of  2.2  to  2.5  per  cell  cost 
about  $10  each.     The  current  may  be  reduced  by  small  ventilated 
rheostats,  one  of  which  is  connected  to  each  independent  group  of 
six  pairs  of  electrode  clamps.     The  wires  leading  to  each  set  should 
be  provided  with  a  special  switch  connection  to  an  ammeter  and 
voltmeter.     The  first  instrument  may  read  up  to  10,  the  latter 
to  5  units. 


ANALYSIS  OF  COPPER 


8.  Electrolytic  Cabinets  are  varied  in  design  according  to 
the  work.  The  Tennessee  and  Cananea  Companies  use  the 
Guess-Haultain  cabinet,  which  is  specially  adapted  to  ore-testing, 
because  the  electrodes  are  made  of  very  thin  corrugated  foil 
and  sand-blasted. 

A  heavier  equipment  is  required  for  the  assay  of  metal.  There 
are  two  systems  in  use  for  connecting  the  individual  assays,  or 
clamps,  to  the  main  wires  from  the  generators.  In  the  first  sys- 
tem, represented  by  the  rack  of  A.  M.  Smoot  (Fig.  4),  or  the 


T5 

.WTfr 

E 

JW42L1L, 

BED 

Vf<)Vf   ^)| 

(%) 

6 

•  ii    iT/.i  " 

y    M 

=Q 

I 


fl 


-)  j:  « 

ife 

a 

a 

A 

==  —  y 

.  a 

^^ 
a 

—y  — 

a 

a 

a 

a  k 

iij 

/•*  Mahogany  fase 
£.-  Aluminum  Ang/e 
0-  Aluminum  Rod 
H- Cut-out  Plugs,  Brass, 
Tops. 


Fig.  4.  —  Rack  for  10  Electrolyses  in  Series. 

cabinet  of  E.  Keller,  the  assays  are  arranged  in  series,  and  a 
plug  must  be  inserted  as  each  assay  is  withdrawn,  to  allow  the 
current  to  pass. 

In  the  second  system,  also  in  general  use,  the  assays  are  ar- 
ranged in  small  sets  of  five  or  six  assays,  in  parallel  connection. 
The  withdrawal  of  any  assay  does  not  break  the  circuit,  but 
causes  the  remaining  assays  to  receive  more  current,  temporarily. 

(a)  Series  System.  —  Mr.  Smoot  has  a  special  device  to  per- 
mit the  rapid  withdrawal  of  electrodes  without  breaking  the 
circuit,  or  permitting  the  contacts,  at  any  time,  to  mar  the 
wires  and  alter  their  weight.  There  should  be  no  exposed  screws 
or  brass  connections  liable  to  corrosion  above  the  assay  beakers. 
The  simple  form  of  rack,  illustrated  in  Figs.  4,  5,  6,  is  arranged 


INTRODUCTION 


A '  Mahogany  Base 
BsAlumirwm  Posf 
C  -  5 fee  I  Spring 
D  *  Hard 'Rubber  Cap 
E  =  Aluminum  Angle 
F- Brass  Machine 
Screw 


to  hold  ten  assays  in  series,  the  maximum  number  which  may  be 

placed  on  one  wooden  bar  of  this  type, 

although  any  number  of  racks  ,may  be 

joined,  according  to  the  voltage  of  the 

available    current.     The    details   of  the 

special  rubber  binding  post  are  shown  in 

Fig.  5. 

The  wires  of  the  electrodes  pass 
through  the  holes  in  the  rubber  caps 
and  are  held  firmly  in  the  V-shaped 
slots  in  the  aluminum  rods  by  the  pres- 
sure of  the  springs,  which  tend  always  to 
push  the  caps  to  one  side.  An  immediate 
release  is  effected  simply  by  pushing  the 
sides  of  the  rubber  caps  against  the 
springs.  There  are  no  wires,  the  current 
being  carried  through  aluminum  or  brass 
rods  of  larger  cross-section.  All  metal 
over  the  beakers  is  protected,  the  con- 
nections being  shown  in  illustrations  No. 
5  and  6.  The  current  of  two  cells  is  em- 
ployed, although  current  from  a  dynamo, 
through  two  rheostats,  may  be  used  instead. 


Fig.  5.  —  Plan  of  Binding 
Post. 


The  wires  from 


Fig.  6.  —  Arrangement  of  Circuit. 


battery  I  pass  through  all  assays.  At  point  P,  a  plug  is  inserted 
connecting  bar  X  with  bar  Y,  and  the  variable  resistance  VR  of 
battery  2  is  regulated  so  that  the  ammeter  A  registers  .40  amperes. 


8 


ANALYSIS  OF  COPPER 


When  it  is  desired  to  remove  the  assays,  remove  plug  P,  thus 
permitting  the  current  from  battery  I  only  to  pass  through  all 
the  tests. 

Insert  a  plug  at  point  S  which  will  permit  both  batteries  to 
supply  assays  2,  3,  4,  etc.,  but  allow  only  the  current  from  bat- 


--*--. 


IP.M!! 


J-LLJ 


_JK_. 


<& 


s\; 


-*$ 


mm 

H.LLLLU-U, 


ILUJAILLV. 


r 


-Side 


Thread  R.H. 


All  fo  be 
Threads  Standard 


Fig.  7.  —  Brass  Electrode  Clamp. 

tery  I  to  pass  through  test  No.  1.  This  device  permits  the  re- 
moval of  the  first  assay  without  cutting  off  the  current  from 
the  others.  By  a  similar  process  the  other  assays  are  withdrawn, 
one  by  one.  If  it  is  desired  to  take  off  one  (say  No.  4)  without 
disturbing  the  others,  it  may  be  done  by  inserting  the  plug  at 


INTRODUCTION 


9 


point  "T,"  thus  short-circuiting  test  No.  4,  which  may  be  with- 
drawn so  quickly  that  no  coppep  ^an  redissolve. 

(6)  The  Parallel  System,  with  tests  arranged  in  small  groups, 
as  adopted  by  the  Calumet  &  Hecla  Laboratories,  and  by  the 
American  Brass  Co.,  seems  to  permit  as  rapid  manipulation  as 
any  rack  yet  designed.  In  the  C.  &  H.  apparatus,  brass  terminals 
rest  upon  a  continuous  shelf  of  hard  vulcanite  —  perforated  with 
small  holes  just  large  enough  for  the  electrode  wires,  so  there  is  no 
chance  for  injurious  corrosion  of  the  terminals,  which  are  soldered 
to  the  insulated  leads.  The  electrode  clamps  are  arranged  in 
pairs  on  the  long  strip  of  vulcanite,  or  hard  rubber,  which  is 


Fig.  8.  — Rack  for  Electrolysis  —  Parallel  System. 

6.3  mm.  thick  and  10  cm.  wide  and  is  supported  on  brackets, 
with  the  under  side  of  the  strip  30  cm.  above  the  main  shelf. 
About  six  pairs  of  brass  terminals  are  connected  in  parallel  with 
two  large  copper  wires  which  lead  directly  to  an  individual  switch, 
rheostat,  and  ammeter  switch.  Assays  may  be  taken  off,  one  by 
one,  without  inserting  any  plugs,  the  current  being  gradually 
reduced  after  each  removal,  by  means  of  the  variable  resistance. 
This  system  consumes  a  little  more  current  than  the  first  or 
series  arrangement. 

The  electrode  clamps  are  made  from  square  brass  rods,  1 
cm.  diameter  and  5  cm.  (2  inches)  in  length.  A  V-shaped  slot 
is  made  on  the  rear  end  of  each,  and  the  conducting  wire,  with 
the  insulation  removed  at  this  point  only,  is  laid  in  the  slot  and 
soldered.  It  may  be  more  convenient,  in  small  installations,  to 


10 


ANALYSIS  OF  COPPER 


employ  as  variable  resistances,  small  banks  of  incandescent  lamp 
sockets,  in  which  may  be  inserted  lamps  of  varied  candle-power, 
or  amperage.  Storage  accumulators  are  conveniently  charged 
through  lamps  as  resistances.  Figs.  7  and  8  show  the  design. 
The  beakers  rest  upon  wooden  spools.  The  manipulation  of  the 
assays  is  described  in  Chapter  XL 

(c)  The  European  Equipment  of  the  Mansfeld  Works  merits 
a  short  description.  According  to  Hermann  Koch,  a  current  at 
3000  volts  is  reduced  by  a  transformer  and  motor-generator  to 
a  100  ampere  current  at  8  volts  tension,  which  is  used  to  charge 


if 


Fig.  9.  — Mansfeld  Electrolytic  Table. 

three  large  accumulators,  furnishing  ordinarily  about  25  amperes 
for  electrolysis  at  the  present  time. 

Fig.  9  illustrates  a  special  table  for  electrolysis. 

The  resistances,  which  reduce  the  tension  to  2-2.8  volts  for 
each  assay,  are  iron  frames  with  12  bobbins.  Special  connec- 
tions give  equal  tension  at  all  electrodes,  independent  of  changes 
in  total  load.  The  ampere  meters  read  up  to  5  amperes  for  each 
group  of  3  to  16  assays.  For  the  final  division  of  the  current 
(.1-.5  ampere  per  assay),  small  marble  slabs  are  fastened  to 
the  back  board,  bearing  two  rows  of  brass  connectors  which  carry 
the  current  to  the  positive  and  negative  clamps  and  tripods. 
The  American  Brass  Co.  use  a  double  system  of  conducting 


INTRODUCTION 


11 


metal  posts,  of  similar  design,  but  connected  below  the  table, 
so  that  the  wiring  is  concealed.  -  A  rheostat  is  provided  for  each 
group  of  five  assays. 


DEVICES    FOR    THE    CIRCULATION    OF    ELECTROLYTES 

9.   Systems   in   General   Use.  —  1st.   Rotation  of  the  anode, 
or  cathode,  by  attachment  to  a  spindle  driven  at  high  speed  by  a 
small  electric  motor.    2d.  Rotation  of  the  solution  in  the  beaker  by 
electro-magnetic  force,  as  in 
the    " Rotary     Device"     of 
Professor  F.  C.  Frary.1     (W. 
B.  Price  has  obtained  good 
circulation  in  brass  analysis, 
by   blowing    compressed   air 
upward  through  a  small  tube 
near  the  anode.) 

For  the  first  system,  a 
good  anode  may  be  made 
from  a  stout  platinum  wire 
to  the  bottom  of  which  is 
clamped  a  round  bladed  pro- 
peller, 2.5  cm.  in  diameter. 
According  to  the  inventor,2 
the  Frary  Solenoid,  or 
"Rotary  Device/'  has  been 
patented  only  in  Germany, 


Fig.  10a.  —  Frary  Rotary  Device. 


but  can  be  obtained  from  the 

Vereinigten      Fabriken     fur 

Laboratoriums-Bedarf ,  Berlin,  —  or  their  agents,    the  Standard 

Scientific  Co.,  New  York. 

Fig.  10a  illustrates  this  model,  and  106  shows  a  modification 
which  the  author  was  obliged  to  devise  some  years  ago  (before 
Professor  Frary's  paper  had  been  noted) ,  in  order  to  accommodate 
a  beaker  12.5  cm.  high  and  5.7  cm.  diameter.  .A  large  size  was 
designed  to  accommodate  a  No.  5  (750  c.c.)  beaker,  and  provided 
with  small  tubes  to  conduct  cold  water  between  the  beaker  and 
the  copper  cylinder  surrounding  it.  The  copper  cylinder  is 
brazed  water-tight  to  an  upper  and  lower  plate  of  soft  steel, 


Z.  Electrochem.,  13  (1907),  308. 


2  Letter. 


12 


ANALYSIS  OF  COPPER 


doff 


forming  a  reel,  which  is  coated  with  mica  and  wound  with  about 

500  turns  of  No.  13  (B. 
&  S.  gauge)  insulated 
copper  wire.1 

The  electric  current 
is  usually  passed  through 
the  electrodes  and  coil  in 
series.  A  magnetic  field 
is  produced  in  the  solu- 
tion which  constantly 
diverts  the  lines  of  force 
passing  radially  from 
anode  to  cathode.  With 
the  largest  size  of  appa- 
ratus, the  author  uses  a 


§5 

>Sfeel  V 

A 

i 

\ 

i 

'cm.  ? 

(Copper  Cylinder 

i 

*\Coil  £00  Turns-  • 

1 

(  No._  13  B&S.  Gage 

i            <Q 

ft*"-  14 

...,  J. 

AN 

2 

Tl 

1 

Knob  or 

Brazed     \ 

i 

/\_J2> 

n±-L 

\ 

!| 

IT  H 

Fig.  106.  —  Sectional  View  of  Water-cooled 
Solenoid. 


cathode  cylinder  of  plati- 
num sheet,  7.5  diameter,  11  cm.  high,  and  perforated  with  holes 
3  mm.  diameter,  spaced  1  cm.  apart. 

EQUIPMENT    FOR    DRILLING    OF    CAST    COPPER 

10.  Strong  power  drills  must  be  used  generally,  and   it   is 
convenient  to  have  one  with  a  gauge  on  the  vertical  spindle. 
Small   direct-connected   electric   drills   are   sometimes  employed 
for  gold  and  silver  bullion. 

For  ingots  and  the  thin  square  plates  recommended  by  Edward 
Keller  for  argentiferous  metal  (Chapter  II),  the  author  uses  boxes 
15  cm.  in  depth,  made  from  TV-mch  sheet  steel,  to  preserve  all  the 
chips  from  the  drill.  The  drill  should  be  free  from  all  traces  of 
oil.  The  ingots,  etc.,  are  easily  held  in  place  by  large  flat  wedges, 
and  the  square  plates  are  supported  by  shoulder  pieces  brazed  to 
the  bottom  sheet,  inside  the  box. 

WEIGHTS 

11.  Standard  Weights.  —  In  regard  to  this  matter,  the  au- 
thor cannot  too  strongly  recommend  that  all  large  laboratories 
preserve  as  a  reference  standard,   a  special  gold-plated  set  of 
double-checked  weights   from    100   g.  to    1    mg.,  to  which   the 
weights  of  all  other  balances  shall  be  periodically  adjusted  by 
the  method  of  substitution. 

1    J.  Ind.  and  Eng.  C.  3  (1911). 


INTRODUCTION  13 

For  the  daily  weighing  of  the  five-gram  samples  of  refined 
copper,  F.  D.  Greenwood  employs  a  special  five-gram  brass 
weight,  which  is  again  placed  6n  the  balance  in  taking  the  weight 
of  the  electrode  and  deposited  Copper.  This  brings  the  total  de- 
ficiency, or  difference  from  the  original  weight  of  copper,  on  the 
milligram  weights  and  rider  (see  Chapter  XI). 


CHAPTER  II 
SAMPLING    AND    CRUSHING 

Treatment  of  the  Subject.  —  A  number  of  the  best  mining 
experts  have  recorded  their  testimony  to  the  fact  that  faulty 
sampling  has  been  the  cause  of  greater  disagreement  and  losses 
than  any  inherent  defect  in  the  assay  methods  usually  employed 
or  any  personal  equation  in  their  operation.  For  the  mathe- 
matical theory  of  the  subject,  any  one  may  consult  the  exhaus- 
tive papers  of  D.  W.  Brunton  (1)  and  S.  A.  Reed  (2)  on  ores,  and 
E.  F.  Keller  for  metallic  copper  (26).  Only  the  regular  practice 
of  mines  and  metallurgical  works  will  be  considered  in  this  chap- 
ter (3).  Whatever  plan  is  locally  adopted,  it  should  furnish  good 
agreement  between  contracting  parties  and,  where  samples  are 
taken  throughout  the  various  mining  and  smelting  operations  of 
any  company,  the  sampling  should  be  done  with  such  care  that 
a  full  exhibit  may  be  made  of  the  absolute  and  relative  gains,  or 
losses,  of  the  successive  operations  of  ore  and  metal  treatment. 

Divisions  of  the  Subject.  —  1.  Mines.  2.  Western  sampling 
mills.  3.  Stamp  mill  control.  4.  Carload  lots  of  ores  at 
eastern  smelters.  5.  Slags  and  copper  products  within  the 
smelting  works. 

DIVISION   1  — MINE    SAMPLING 

1.  In  the  valuation  of  prospects  and  control  of  mines  by 
sampling  and  assaying  there  are  three  general  systems.  For  a 
full  description  several  papers  are  listed  at  the  end  of  the  chapter 
where  all  the  references  are  tabulated.  The  general  opinion  of 
the  best  authorities  is  made  the  basis  of  the  directions  outlined. 

System  A.  —  The  selection  of  a  large  number  of  small  samples, 
cut  quickly  across  the  vein,  at  points  evenly  placed  in  parallel 
lines  across  the  whole  area,  as  exposed.  The  first,  and  least 
expensive,  system  gives  correct  results  only  on  soft  ores  of  uni- 
form grade  and  is  used  for  testing  new  stopes,  etc.,  in  producing 
mines  of  uniform  character.  The  grooves  are  made  about  3 


SAMPLING  AND  CRUSHING  15 

inches  (7.5  cm.)  in  width  and  6  inches  deep  in  soft  ores  or  about 
1  inch  deep  in  quartz,  and  finally  trimmed  to  uniform  size. 

System  B.  —  A  smaller  number  of  heavy  samples,  at  equal 
distances  but  farther  apart,  aod  large  enough,  if  blasting  of 
grooves  is  absolutely  necessary,  to  represent  all  the  variations 
along  the  lines  of  cutting.  Such  a  sample,  in  operating  proper- 
ties, may  weigh  from  25  to  50  tons  to  represent  a  stope,  although 
with  new  properties,  the  usual  amount  is  50  to  400  pounds 
(Kir by).  Philip  Argall  assumes  5  pounds  per  foot  across  10 
feet  of  vein,  or  stope.  This  system  is  advisable  for  all  American 
hard  ores,  where  the  values  are  very  uneven  and  is  the  most 
frequently  employed  for  accurate  valuation. 

System  C  consists  of  actual  "mill  runs"  of  lots  of  50  tons,  and 
more,  of  regularly  mined  ore  from  each  stope,  or  chute.  The 
sample  may  be  cut  out  by  mechanical  sampling  mill  after  the 
ore  has  left  the  mine.  Such  a  large  works  sample  is  necessary 
for  native  copper  (see  description  by  G.  H.  Benedict  [7] ). 
Even  such  tests  may  be  deceptive  with  regard  to  the  quality  of 
ore  that  can  be  regularly  produced. 

2.  Practical  Notes.  —  These  are  based   on   papers  of   E.  P. 
Mathewson,  D.  W.  Brunton,  and  others.     Ordinary  duck,  etc., 
will  catch  wire  gold,  or  copper  metal.     The  best  cloth  to  use  for 
mine  rock,  where  the  pieces  are  small,  is  soft  flexible  enameled 
oil  cloth.     Samples  of  over  one  ton,  and  made  up  of  pieces  at 
least  three  inches  in  diameter,  may  be  reduced  at  the  mine  to 
one  ton  by  throwing  aside  every  tenth  shovel,  if  the  work  must 
be  done  by  hand.     Such  fractions  are  then  reduced  to  one-half 
inch   size,   and   five  to  fifty  pounds   weight,   by   crushing   and 
dividing. 

A  hammer  tends  to  break  off  hard  projections,  while  a  geolo- 
gist's hammer  seeks  the  soft  spots;  hence  the  best  tool,  in  the 
opinion  of  many  experts,  is  a  moil  struck  by  a  four-pound  hammer. 

The  sampling  stations  should  be  tied  to  the  survey  stations 
on  the  mine  maps  to  permit  re-sampling.  A  conservative  defi- 
nition of  the  phrase  "ore  developed"  is  that  it  means  ore 
exposed  on  four  sides. 

METHODS    AT    THE    MANSFELD    MINES 

3.  At   Mines.  —  The   largest   mines   of    Germany  still   find, 
after  eighty  years'  experience,  that  the  first  system,  A  is  best 


16  ANALYSIS  OF  COPPER 

suited  to  their  conditions.  A  description  of  the  system,  by 
H.  Koch,  has  been  necessarily  condensed  in  translation.  The 
sampling  of  the  hoisted  ore  (including  the  mineral  typolite 
and  shales  from  the  quarries)  is  carried  out  at  both  the 
shafts  and  the  smelter,  so  that  the  same  smelting  stock  is 
examined  twice.  The  necessity  for  this  procedure  arises  from 
the  exceedingly  variable  nature  of  the  slates.  Only  an  average 
result  of  the  metallic  contents  of  the  doubled  samples  can  be 
considered  accurate,  although  the  metal  can  be  closely  determined 
in  each  one  as  received.  The  samples  at  the  shafts  are  taken  by 
small  scoops  or  troughs  out  of  the  mine  cars  or  cable-buckets, 
while  they  are  being  filled,  and  in  such  proportion  that  the  total 
weight  of  sample  amounts  to  nearly  ^iir  of  the  ore  hoisted. 

The  material,  keeping  that  from  the  quarries  and  mines 
separate,  is  united  to  form  daily  catch  samples  from  each  shaft, 
stamped  or  crushed  in  machines,  pulverized,  sifted,  well  mixed, 
reduced  to  about  one  hundred  grams,  and  then  examined 
by  color  test  to  assign  its  grade  as  to  copper  (assay  weight, 
2  g.) .  From  the  same  samples,  one  gram  is  taken  (for  each  metric 
ton  loaded),  to  form  a  weekly  catch  sample,  which  again  is  re- 
duced, mixed  and  graded  as  to  copper  contents  by  the  colori- 
metric  test;  then  delivered  to  the  central  laboratory,  where  the 
accurate  determination  of  the  copper  and  silver  is  completed 
by  electrolysis  and  cupellation. 

4.  At  the  Smelting  Works,  samples  are  taken  during  the  dis- 
charge of  the  ore  cars  from  the  mines,  and  are  collected  sepa- 
rately from  each  shaft  or  quarry  to  constitute  daily  quarry  and 
mine  samples,  which  are  ground  down  as  at  the  mines  and  tested 
colorimetrically.  For  each  ton  of  ore  received  one  gram  is  re- 
served for  a  monthly  sample,  and  this  material,  after  proper  mix- 
ing and  reduction,  is  tested  by  color  test  at  the  mines,  and  by 
gravimetric  analysis  at  the  smelter. 

The  values  obtained  from  the  monthly  average  samples  taken 
at  the  smelter  are  compared  with  the  monthly  averages  com- 
puted from  the  weekly  average  test  samples  taken  at  the  shafts. 
The  arithmetical  mean  of  the  mine  and  smelter  samples  is. taken 
as  the  basis  of  the  office  reports.  To  judge  of  the  (probable) 
values,  frequent  tests  are  also  made  of  gossan,  and  surface  strata, 
and  assayed  partly  by  color  at  the  mine,  partly  for  copper  and 
silver  at  the  main  laboratory. 


SAMPLING  AND  CRUSHING  17 

Raw  Ore  from  Smelting  Ore-beds.  —  When  a  stream  of  ore  is 
cut  out  of  the  bedding-pile,  9  to  J.O  spoon  samples  are  taken  (5  to 
6  from  each  cut  of  7  metric  ifons),  and  collected  as  one  sample 
until  25  tons  are  smelted.  This  Average  unit  sample  (reduced  to 
about  200  g.)  goes  to  the  laboratory  for  the  valuation  of  the 
copper  and  silver  contents. 

From  the  finished  samples,  a  monthly  average  sample  is  made 
up  for  complete  analysis. 

DIVISION    2  — MECHANICAL    SAMPLING 

5.  The  daily  control  of  the  large  western  mines  is  effected 
by  diverting  a  fixed  proportion  of  the  daily  product  of  the  mine 
(perhaps  one-tenth  of  the  cars  if  the  ore  is  uniform)  to  a  sampling 
mill,  located  at  the  smelter,  or  at  the  mill  if  the  ore  requires 
concentration.  , 

At  the  Anaconda  Mines,  Montana,  the  sample  lots  of  ore 
are  elevated  to  bins  at  the  top  of  the  sampling  building,  and  then 
passed  down  through  an  alternating  succession  of  rolls,  crushers, 
and  four  Vezin  samplers  until  the  ore  is  cut  to  a  portion  of  3.2 
pounds  for  each  ton  of  the  original  sample.  ixix£x£  =  BTS 
and  sib  X  2000  =  3.2.  The  new  five-story  mill  of  the  Calumet 
&  Arizona  will  reduce  a  ton  by  four  Snyder  machines  to  1.6  or 
3.2  pounds,  according  to  the  nature  of  the  ore  sampled. 

The  product  of  the  mechanical  samplers  is  further  reduced 
on  an  iron  floor  by  Brunton  shovels.  The  Garfield  smelter  is 
said  to  reduce  the  ore  by  causing  the  sample  to  be  heaped  into 
cones  which  are  flattened  and  divided  by  iron  crosses  against 
which  the  material  is  shoveled.  These  crosses  are  made,  in 
several  sizes,  from  lOx-rV  inch  iron  plates  of  suitable  lengths, 
set  vertically.  (A  short  discussion  of  the  requirements  of  a 
good  sampler,  and  of  Eastern  practice,  is  given  in  13,  Division 
4.) 

When  the  sample  is  reduced  to  100  or  even  25  pounds  (vary- 
ing with  the  locality)  the  ore  is  dried  on  a  steam  drier  to  deter- 
mine the  moisture,  and  the  dry  material  put  through  an  Engelhardt 
sample  grinder,  divided  by  riffles,  bucked  to  pass  a  100-mesh  sieve 
(100  to  the  linear  inch),  and  put  in  four  packages  of  6  to  12  ounces 
each.  One  goes  to  the  laboratory,  one  to  the  owner  of  the  ore, 
and  two  are  filed  away  in  case  of  dispute.  In  some  works  the 
product  of  the  last  machine,  reduced  to  100  or  even  25  pounds, 


18  ANALYSIS  OF  COPPER 

goes  direct  to  the  laboratory  for  all  the  further  reduction  and  mois- 
ture test.  There  it  is  ground,  quartered,  and  riffled  down  to  about 
50  ounces  by  a  fixed  rule,  which  must  be  the  result  of  experiment 
with  different  classes  of  ores.  The  rule  actually  depends  on  the 
principle,  that  during  the  reduction  of  the  ore  by  grinding,  sift- 
ing, and  quartering,  there  is  in  each  successive  product  a  fixed 
ratio  of  the  largest  particles  of  valuable  metal,  or  sulphides,  to 
the  whole  weight  of  each  size  which  must  not  be  exceeded  or  the 
final  error  will  be  too  great,  i.e.,  quartering  must  not  be  carried 
too  far,  before  grinding  finer.  The  separation  of  the  fine  and 
coarse  particles  in  transit  through  the  modern  mechanical  sam- 
pling mill  is  taken  care  of  satisfactorily  by  reducing  the  length  of 
the  spouts  between  cutting  devices,  and  using  a  shaking  feed  for 
all  crushers  and  rolls.  Any  metallics  on  the  sieves  are  weighed 
along  with  the  ore  portion  from  which  they  were  taken  and  sep- 
arately assayed,  unless  they  can  be  ground  in  with  the  ore  by 
passing  through  the  grinder  a  second  time. 

IRON    FROM    GRINDING    PLATES 

6.  Iron  is  introduced  into  all  hard  ores,  when  finely  pulver- 
ized by  steel  plates.     In  furnace  slags,  the  iron  derived   from 
wear  may  amount  to  0.3  per  cent.     To  make  a  correction  factor, 
pass  some  of  each  class  of  material  through  crusher,  and  reduce 
in  large  porcelain  mortar,  and  agate,  or  Abbe  ball  mill.     Compare 
the  iron  in  this  sample  with  the  other. 

DIVISION    3— SAMPLING    IN    STAMP    MILLS 

7.  Concentrates    in  Western    mills  are  passed  through  me- 
chanical samplers.     The  following  description  by  C.  H.  Benedict, 
of  the  sampling  in  the  Calumet  &  Hecla  Stamp  Mills,  illustrates 
a  correct  principle,  adapted  to  the  study  and  control  of  milling 
operations  in  any  district. 

There  is  no  custom  milling,  as  generally  accepted,  on  Lake 
Superior.  A  mine  without  a  mill  leases  the  exclusive  use  of 
one  or  more  stamp  heads  and  owns  the  product.  In  this  way, 
there  is  no  necessity  of  sampling  mills,  if,  in  fact,  the  nature  of 
the  rock  made  such  sampling  possible.  The  quality  of  the  rock 
is  found  by  adding  the  assay  value  of  the  concentrates  to  that  of 
the  tailings. 


SAMPLING  AND  CRUSHING 


19 


In  order  to  test  out  a  given  milling  process,  however,  tests 
are  frequently  made  by  taking  samples  of  all  products  for  a  week 
on  amygdaloid  (or  if  on  conglomerate  rock,  about  four  days), 


Discharge 


Fig.  11.  —  Sampler  for  Mill  Tailings. 

in  order  to  get  the  variations  in  stamping.  During  such  tests, 
samples  are  ordinarily  taken  of  each  product  for  one  second  every 
hour.  For  the  overflow  of  jigs,  the  sampler  makes  use  of  a  long 
shallow  iron  trough, "  U  "  shaped,  and  a  little  longer  than  the  width 
of  the  jig,  holding  the  trough  cross- wise  under  the  whole  stream 


20  ANALYSIS  OF  COPPER 

for  the  time  specified.  "From  these  time  samples,  the  calculated 
tonnage  must,  of  course,  check  closely  with  the  car  weights  of 
the  rock,  originally  stamped."  Concentrates  are  weighed  in  bulk 
and  tested  in  one  of  two  ways  —  by  means  of  a  slotted  sampling 
pipe  —  or  by  the  "spoon  and  shovel."  In  the  first  case,  a  f-inch 
(1.9  cm.)  pipe  (with  a  slot  cut  out  in  the  side  and  one  edge  faced 
out  to  make  a  projecting  lip)  is  driven  into  the  car  of  wet  mineral, 
the  pipe  turned,  and  the  resulting  sample  shaken  out  into  long 
pans.  In  the  second  method,  a  portion  is  taken  by  a  spoon,  or 
similar  device,  from  a  shovelful,  at  regular  intervals.  Mid- 
dlings are  sampled  in  the  same  way  as  the  tailings. 

8.  Tailings  of  the  Calumet  &  Hecla  Mining  Co.  are  all  ele- 
vated by  sand  wheels  and  leave  the  mill  in  a  launder  54  inches 
(1.37  m.)  wide,  and  with  a  stream  about  8  inches  deep.  A  sample 
from  this  launder  is  taken  every  hour  and  a  half,  day  and  night, 
by  means  of  the  slotted  sampling  machine  shown  in  Fig.  11. 

This  sampler  consists  essentially  of  a  fan-shaped  receptacle 
with  a  slotted  end,  which  is  carried  through  the  stream  by  being 
suspended  on  a  track  over  the  stream  (and  is  afterward  hoisted 
by  the  spindle,  in  order  to  discharge  it  over  the  edge  of  the  launder 
into  a  metal  barrel).  The  samples  from  each  shift  are  then  com- 
bined, and  should  be  dried  in  large  tarred  pans  over  steam  coils, 
then  screened  through  a  succession  of  sieves  (of  10,  20,  40,  and  60 
meshes  to  the  linear  inch).  The  resulting  fine  products  are 
weighed,  sampled,  and  the  calculated  assay  from  the  sizings 
checked  up  against  the  original  assay. 

Laboratory  reduction  of  these  samples  of  tailings,  or  mineral, 
is  accomplished  ordinarily  by  permitting  the  dried  sample,  if 
large,  to  flow  through  a  hopper,  and  cutting  the  resulting  stream 
of  dry  pulp  with  a  rectangular  pan,  moving  in  time  with  a  pen- 
dulum. If  the  sample  is  small  it  is  poured  through  a  funnel,  held 
in  the  hand  over  cut-out  riffles. 

The  size  of  the  sample  for  the  assayer  is  regulated  by  the 
coarseness  of  the  material,  and  is  usually  about  40  grams.  This 
is  crushed  through  a  60-mesh  sieve,  the  resulting  metallics  picked 
out  to  constitute  a  separate  sample,  and  the  fines  reduced  to 
portions  of  5  grams  for  electrolytic  assay.  The  combined  assay 
values  of  tailings  from  the  different  machines  must  check  with 
the  assay  of  the  general  tailings  from  the  main  waste  launder. 


SAMPLING  AND  CRUSHING  21 

DIVISION    4  — SAMPLING    AT    REFINERIES 
* 

9.  Mill   concentrates  of   native  copper   are  sampled  in  the 

refinery  from  hand  carts;  or  from  chutes,  when  weighed  out  to 
the  furnaces,  taking  say  two  small  cups  for  each  thousand 
pounds  of  the  wet  product. 

The  daily  samples  from  each  grade,  and  from  each  mine,  are 
kept  in  water-tight  copper  cans,  inclosed  in  a  water-tight  wooden 
box,  until  the  percentage  of  water  and  copper  can  be  determined. 

At  Custom  Sampling  Works,  New  York  (By  A.  M.  Smoot).  — 
There  should  be  no  invariable  rules  for  the  sampling  of  copper 
ores  and  mattes,  because,  while  the  grade  and  physical  condition 
are  the  principal  factors  in  determining  the  procedure,  varying 
conditions  of  sale  and  delivery  must  also  be  considered. 

10.  Hand  Sampling.  —  Low-grade  copper  ores,  containing  only 
small  amounts  of  gold  and  silver,  may  be  conveniently  tested 
in  100-ton  lots.     If  the  ore  shows  no  pieces  larger  than  4  inches 
(10  cm.)  diameter,  take  every  tenth  barrowful  as  it  is  discharged 
from  cars,  or  every  tenth  bucketful  as  it  is  taken  from  vessels, 
and  set  it  aside  for  a  sample. 

Crush  the  10  per  cent  sample  to  2-inch  size,  or  5  cm.  diameter, 
and  by  half  shoveling,  reduce  it  to  five  tons  (or  4536  kg.).  Crush 
this  to  1  inch  (2.5  cm.)  diameter,  and  reduce  it  again  by  half  shov- 
eling to  one  and  a  quarter  tons.  Crush  to  |  inch  and  reduce  by 
shovel  to  625  pounds  (284  kilos).  Crush  to  \  inch  (or  4.2  mm.) 
diameter,  and  reduce  by  half  shoveling,  or  preferably  by  riffling, 
to  about  80  pounds  (36  kilos),  crush  to  pass  a  sieve  of  16  meshes 
to  the  linear  inch  and  reduce  by  riffling  to  about  five  pounds 
(2.3  kilos).  Reduce  this  to  pass  an  80-  or  100-mesh  sieve,  mix  well, 
and  divide  by  riffling  into  the  required  number  of  sample  packages. 
Quartering  should  be  avoided,  since  it  may  easily  lead  to  errors 
which  will  tend  constantly  in  one  direction.  It  is  more  laborious 
and  costly  than  half  shoveling. 

11.  Rich  Ores,  containing  appreciable  gold  and  silver  values, 
as  well  as  high  copper,  should  be  divided  into  fifty  or  even  twenty- 
five  ton  lots  (22.7  metric  tons)  for  sampling,  unless  they  are  very 
uniform.     If  possible,  all  rich  ores  should  be  crushed  to  2  inches 
(5  cm.)  diameter  before  any  division  is  attempted.     Take  every 
fifth  shovelful  as  a  sample,  crush  to  f  inch  (1.9  cm.),  and  reduce  by 
half  shoveling  to  2J  tons,  crush  to  \  inch  (6.3  mm.),  and  reduce  to 


22  ANALYSIS  OF  COPPER 

five  hundred  pounds,  crush  to  pass  eight  meshes  to  the  linear  inch 
and  reduce  to  fifty  pounds;  then  crush  to  pass  20  mesh  and  reduce 
to  five  pounds  (2.27  kilos).  Grind  this  through  a  100-mesh  sieve 
(39  meshes  per  cm.),  mix  well,  and  divide  into  the  required  number 
of  assay  samples. 

12.  Mattes.  —  These  are  sampled  like  rich  ores,  but  some 
material  with  high  gold  and  silver  values  will  require  finer  crush- 
ing throughout  and  more  intimate  mixing  between  the  reductions. 
See  note  on  western  methods. 

Duplicate  samples  of  such  rich  mattes  should  be  taken  from 
the  very  beginning  of  the  operations.  Duplicates,  which  are 
made  by  dividing  a  single  sample  at  some  point  toward  the  end 
of  the  coarse  crushing,  only  serve  to  check  the  final  work.  Dupli- 
cates are  especially  desirable  with  very  variable  material;  for 
instance,  where  two  or  three  small  lots  of  widely  different  char- 
acter are  to  be  sampled  as  one  lot.  In  such  cases  as  this  all  of 
the  material  should  be  crushed  to  at  least  f  inch  (1.9  cm.),  and 
mixed  by  coning  before  any  subdivision  is  attempted. 

Fine  crushing  throughout.  —  It  is  the  practice  at  some  eastern 
works  to  crush  the  whole  ten  or  twenty  per  cent  sample  from  the 
original  lot  to  J  inch  (6.3  mm.),  and  then  by  repeated  mixing  and 
half-shoveling  to  reduce  it  at  once,  without  further  crushing,  to 
250  or  300  pounds.  This  is  done  on  the  ground  that  it  is  cheaper 
to  crush  the  whole  sample  than  to  introduce  several  intermediate 
samples  of  coarser  materials. 

The  crushing  of  the  whole  lot  is  insisted  upon  by  one  or  two 
western  plants,  when  a  car  is  loaded  with  a  mixture  of  reverbera- 
tory  and  cupola  furnace  mattes.  Although  a  satisfactory  sample 
is  obtained,  the  production  of  a  large  amount  of  fines  is  often 
objectionable  to  the  smelter.  If  care  is  used  throughout  in  hand 
sampling,  the  results  are  accurate,  but  treatment  of  large  lots  is 
too  slow  and  costly. 

NOTE.  —  Western  mechanical  practice  has  been  outlined  under 
Division  2. 

13.  Machine  Sampling.  —  For  large  lots  of  uniform  material, 
machines  are  more  economical  and  practicable,  as  stated  in  the  ac- 
count of  the  systems  of  the  western  reduction  works.    The  obser- 
vation of  several  important  points  in  construction  and  operation 
(which  were  not  mentioned  under  mill  practice)  is  essential  to  good 


SAMPLING  AND  CRUSHING  23 

work.  The  sampler  should  be  constructed  so  that  the  scoops  or 
diverters  cut  the  whole  ore  stream  at  frequent  intervals.  The 
scoops  should  permit  a  free  fall  to.  the  stream  after  it  is  cut  out,  so 
that  it  shall  not  be  retarded  and  so  no  pieces  shall  bounce  outside. 
The  openings  in  the  scoops  or  diverters  should  be  at  right  angles 
to  the  ore  stream,  and  they  should  move  across  it  with  uniform 
speed,  and  at  uniform  intervals.  The  openings  should  be  at 
least  four  times  the  diameter  of  the  largest  pieces  which  pass 
through  them. 

In  machines  such  as  the  Vezin,  in  which  the  sample  scoops 
revolve  around  a  shaft,  the  shape  of  the  scoops  should  be  sectors 
of  a  circle  whose  center  is  the  center  of  the  shaft.  The  feed  to 
the  machine  and  the  flow  of  the  ore  should  be  constant  and  uni- 
form. The  whole  apparatus  should  be  housed  to  prevent  the 
escape  of  dust,  and  at  the  same  time  all  parts  should  be  easily 
accessible.  As  in  western  mills,  the  final  product  of  the  machine 
sampler  passes  to  a  closed  box,  or  car,  from  which  it  is  taken  to  a 
sampling  floor  and  finished  by  hand.  Ordinarily  50  tons  would  be 
cut  by  three  machines  to  800  pounds.  The  last  machine  sample 
would  then  be  cut  with  a  Jones  riffle  to  400  pounds,  crushed  to 
12  mesh,  and  riffled  to  50  pounds.  Finally,  crush  to  20  mesh  and 
riffle  to  5  pounds,  grind  this  to  100-mesh  sieve,  mix  and  divide 
it  into  the  required  number  of  samples. 

14.  Moisture  Samples.  —  This  question  is  very  important, 
especially  in  ores.     Since  all  ores  and  mattes  are  assayed  on  the 
dry  basis  and  settlement  is  based  on  the  dry  weight,  moisture 
samples  should  be  taken  at  the  time  of  weighing.     Weighing  is 
generally  done  immediately  before  sampling.     For  a  moisture 
sample,  at  least  10  kilograms  of  ore  should  be  taken  after  crush- 
ing to  at  least  one-half  inch,  or  preferably  finer,  but  too  much 
crushing  should  be  avoided.     The  reject  from  the  third  mechani- 
cal crushing  of  the  general  sample  usually  affords  a  good  moisture 
sample.     Small  moisture  samples  are  useless. 

DIVISION    5  — FURNACE    PRODUCTS 

15.  Reverberatory   Slags.  —  Waste   ore   slags   from   matting 
furnaces  can  be  taken  at  the  door,  or  sluice,  about  once  in  2  hours, 
or  when  skimming.     Mineral  slags  from  native  copper  contain 
15-20  per  cent  of  copper  as  silicate  and  shot  metal  and  the  last  re- 
fining slags  are  full  of  carbon,  so  that  the  best  average  is  ob- 


24  ANALYSIS  OF  COPPER 

tained  by  breaking  all,  or  a  half  at  least,  of  the  cooled  cakes  from 
the  slag  buggies  and  taking  pieces  of  equal  size  from  the  top, 
middle,  and  bottom  of  each  block  broken. 

16.  Matte  in  Western  Works.  —  Small  hand-ladles  can  be 
filled  at  the  settler  or  hot  metal  ladle  while  tapping,  or  pieces  can 
be  taken  by  shoveling  from  the  cool  material,  after  crushing,  if 
it  is  to  be  bagged  for  direct  shipment.     As  already  noted,  some 
experts  advise  a  preliminary  fine  crushing  of  the  whole,  in  the  case 
of  a  car  of  mixed  reverberatory  and  cupola  matte. 

17.  Cupola  Waste  Slags.  —  The  method,  sometimes  adopted, 
of  dipping  an  iron  rod  in  the  slag  stream,  and  chilling  it  in  water, 
does  not  show  the  average  amount  of  shots  of  metal,  or  prills  of 
matte.     To  secure  an  average  sample,  a  small  hand-ladle  should 
be  held  under  the  full  slag  stream,  and  the  contents  quickly 
granulated  with  water  in  an  iron  pail,  kept  in  a  safe  place.     At 
Lake  Superior,  samples  are  taken  once  an  hour  and  combined 
into  one  sample  for  each  working  shift. 

18.  Anode  Slags  (H.  D.  Greenwood).  —  The  small  slag  pots 
are  dumped  and  the  shells  cooled  with  water,  which  will  help  to 
disintegrate  the  large  pieces.     The  large  pieces  are  then  broken 
up  with  hammers  and  sent  through  the  crushers,  where  they  are 
crushed  to  one-half,  or  one  inch,  pieces,  all  me  tallies  being  returned 
to  the  furnaces.     The  sample  is  coned  and  worked  down  by 
hand  to  about  200  pounds  (or  90.7  kilos) ;  then  crushed  finer  and 
worked  down  to  a  laboratory  sample,  recrushing  finer  with  each 
division.     The  metallics  of  each  quartering  are  kept  separate  (as 
in  the  case  of  Lake  Superior  slags),  and  sampled,  assayed,  and 
proportioned  accordingly. 

19.  Sampling  of  Molten  Copper.  —  Edward  Keller  and  others 
have  proved  that  the  difficulty  of  sampling  pigs  and  other  irregular 
deep  castings  at  anode  furnaces  is  eliminated,  if  thin  square  plates 
are  cast  with  a  full  hot  ladle  directly  from  the  molten  charge,  after 
it  is  well  mixed  and  ready  to  pour  into  molds.     Keller  l  recom- 
mended that  a  plate,  15  inches  square  by  one  inch  in  thickness, 
should  be  taken  from  the  middle  of  each  third  of  the  charge  as 
it  was  tapped  from  the  furnace.    With  refined  native  copper,  it 
has  been  proved  that  plates  6  x  6  x  \  inch  are  large  enough. 
A  uniform  number  of  holes  should  be  drilled  through  each  plate, 
but  the  sampler  should  keep  away  from  the  edges  for  a  distance 

1  Trans.  A.  I.  M.  E.  27  (1897),  106. 


SAMPLING  AND  CRUSHING  25 

equal  to  twice  the  thickness  of  the  plate,  at  least.  A  granulated 
shot  sample,  or  one  of  the  thin  plates,  may  be  correct  for  gold 
and  silver  if  all  skulling  is  avoided  by  pouring  from  a  hot  clean 
ladle.  Keller  insists  that  large  snot  samples  should  be  re-melted, 
if  variable,  and  a  sample  cast  or  granulated.  The  copper  per- 
centage, when  determined  upon  the  shot,  cannot  be  as  good  an 
average  of  a  lot  as  a  result  obtained  from  the  plates,  owing  to  the 
absence  of  some  surf  ace  oxides  which  should  be  included  in  this  case. 
Superintendent  William  Wraith,  of  the  Washoe  Smelter,  con- 
cluded, after  many  tests,  that  the  pouring  of  shot  from  a  hand- 
ladle  tends  to  give  high  results  for  silver.  His  statement  follows : l 

"The  only  method  of  furnace  sampling  which  uniformly  checks  results 
obtained  by  drilling  every  fourth  anode  by  a  99-hole  template  system  con- 
sists in  batting  out  samples  from  the  molten  stream  of  metal,  while  pouring, 
and  allowing  the  copper  to  fall  into  water. 

"The  first  sample  is  batted  from  the  stream  with  a  wooden  paddle, 
30  minutes  after  starting  to  pour,  three  other  samples  being  taken  at  one- 
hour  intervals,  each  portion  weighing  from  4  to  6  ounces.  These  samples 
are  dried,  examined  for  burnt  wood,  screened  on  a  10-mesh  screen  of  No.  8 
wire,  to  remove  fines,  the  oversize  then  screened  on  a  4-mesh  screen  of  No. 
20  wire,  to  remove  the  coarse,  the  undersize  of  this  screen  being  taken  as  the 
sample.  The  four  portions  are  thoroughly  mixed,  and  split  in  half  by  passing 
over  a  16-slot  splitting  device,  slots  being  0.5  inch  wide,  one-half  being  kept 
as  a  reserve  sample,  and  one-half  assayed." 

SLABS    AND    ANODES 

20.  (From  A.  M.  Smoot,  F.  Andrews,  and  H.  D.  Greenwood.) 
—  The  method  of  A.  M.  Smoot,  for  the  custom  sampling  of  pig 
copper  and  anodes,  is  presented  first,  as  it  gives  a  full  explanation 
of  the  reasons  for  every  step  taken  by  the  large  refineries  in  this 
rather  difficult  problem.  Nearly  all  custom  refineries  adopt  the 
same  principle. 

The  template  system  of  sampling  takes  into  account  the  segrega- 
tion of  the  constituents  which  occur  when  any  molten  alloy  is 
cast  into  a  mold  and  chilled.  The  word  "bar,"  as  used  here, 
includes  any  commercial  shapes  into  which  crude  copper  is  cast 
for  shipment.  By  this  system,  the  top  and  bottom  surfaces  of 
any  given  bar,  cake,  or  slab  are  divided  into  a  number  of  squares, 
each  of  which  is  a  bounding  surface  either  of  a  parallelopipedon 
or  a  wedge.  By  drilling  holes  in  the  centers  of  these  squares, 

1  Trans.  A.  I.  M.  E.  41  (1910),  318. 


26  ANALYSIS  OF  COPPER 

clear  through  the  bars,  borings  representing  the  contents  of  the 
solid  figures  are  obtained.  By  making  the  squares  small  and 
drilling  a  large  number  of  holes  in  rotation,  an  accurate  sample 
representing  the  metallic  contents  of  any  given  bar  may  be  ob- 
tained. An  accurate  sample  of  the  lot  may  be  obtained  by  tak- 
ing a  large  number  of  bars  of  the  same  shape  and  character,  and 
drilling  successive  holes,  one  in  each  bar,  each  corresponding  in 
position  to  one  of  a  series  of  squares  marked  off  on  the  top  of 
a  single  bar,  that  is,  by  advancing  the  drill  one  hole  in  the 
template  with  each  successive  bar.  The  number  of  bars  taken 
to  represent  a  lot  should  depend  on  the  number  of  bars  in  the 
lot  and  on  the  character  and  tenor  of  the  crude  copper.  In  ship- 
ments made  up  of  several  converter  charges  of  varying  gold  and 
silver  contents,  all  of  the  bars  should  be  drilled. 

When  the  material  is  of  nearly  even  composition,  such  as  the 
product  of  a  smelter  handling  uniform  ore  from  a  single  mine  or 
district,  a  smaller  proportion  (for  instance  one-fourth  or  even 
one-tenth)  of  the  bars  will  represent  the  lot.  In  sampling  copper 
which  is  high  in  gold  and  silver,  even  when  it  is  of  fairly  uniform 
grade,  every  bar  should  be  drilled.  When  a  fraction  of  the  num- 
ber of  bars  in  a  lot  is  taken,  the  number  should  correspond  with 
the  number  of  holes  in  the  template  or  to  some  even  multiple  of 
this  number,  so  that  one  or  more  complete  cycles  shall  be  used 
and  every  hole  in  the  template  be  represented  in  the  sample. 
This  is  not  important  where  a  number  of  successive  lots  of  the 
same  material  are  sampled.  In  such  cases,  the  rotation  of  drill 
holes  may  overlap  from  one  lot  to  the  next.  (Refer  to  Andre ws's 
account.) 

Since  segregation  on  cooling  takes  place  quite  uniformly 
from  or  towards  every  cooling  surface,  a  quarter  or  half  a  bar 
may  be  assumed  to  contain  all  the  elements  of  segregation  and  a 
quarter  or  half  section  template  may  be  used.  This  is  advanta- 
geous because  a  larger  number  of  small  squares  may  be  laid  out  on 
the  smaller  templates,  and  still  keep  the  same  number  of  holes 
within  the  number  of  bars  to  be  drilled.  In  drilling  bars  with  a 
flange  or  wedge,  the  template  should  be  laid  out  so  that  the  weight 
of  borings  from  the  wedge-shaped  part  of  the  bar  is  in  the  same 
ratio  to  that  taken  from  the  rectangular  part  as  the  weight  of  the 
wedge  portion  is  to  the  weight  of  the  rectangular  portion.  All 
holes  are  usually  drilled  with  a  half-inch  (1.27  cm.)  drill,  and  must 


SAMPLING  AND  CRUSHING  27 

extend  clear  through  the  bar.  Too  much  emphasis  cannot  be 
laid  on  this  point.  The  drill  should  be  driven  at  high  speed  with 
a  light  feed,  so  that  the  drillings  may  be  thin  and  easily  ground. 
Forcing  the  drill  produces  thick  drillings. 

The  top  surface  of  crude  copper  is  usually  very  rough  from 
the  escape  of  gases,  especially  in  the  central  portion.  The  top 
surfaces  at  the  edges  are  usually  fairly  smooth.  The  rough  top 
surface  frequently  contains  undecomposed  matte  and  sometimes 
small  pieces  of  slag,  as  also  an  excess  of  cuprous  oxide.  As  cuprous 
oxide  is  a  solvent  for  silver,  the  top  skin  of  crude  copper  bars  is 
frequently  higher  in  silver  than  the  underlying  metal.  It  is,  of 
course,  poorer  in  copper. 

In  drilling  bars  with  the  top  surface  up  —  or  towards  —  the 
drill,  some  of  the  smaller  particles  of  the  borings  become  lost  in 
the  interstices  of  the  rough  surface;  they  cannot  be  completely 
collected.  The  smaller  particles  consist  in  part  of  the  brittle 
top  surface;  thus  drillings  from  rough  bars  made  with  the  top 
surface  up  are  not  an  average  sample.  When  bars  are  drilled 
with  the  bottom  surface  up,  the  pressure  of  the  drill  is  apt  to  break 
off  rather  large  pieces,  forming  craters  in  the  brittle  crust  when 
the  drill  is  thrust  through  the  bar.  It  is,  therefore,  customary  to 
drill  half  of  the  sample  bars  with  the  tops  of  the  bars  up  and  half 
in  the  reverse  position.  The'  drill  holes  in  the  wedge  must  neces- 
sarily be  taken  with  the  top  of  the  bar  uppermost. 

Shipment  of  Samples. —  Containers  for  powdered  ore  or  drill- 
ings of  crude  copper  usually  consist  of  sacks,  stout  manila  paper 
bags,  or  printed  envelopes  with  patent  fasteners.  Drillings  of 
refined  copper  should,  however,  always  be  kept  in  tight  glass- 
stoppered  bottles  and  shipped  in  capped  bottles  in  special  mailing 
cases  to  provide  absolute  protection  from  oxidation  in  transit. 

21.  Reduction  to  Assay  Sample. —  The  weight  of  drillings 
from  the  usual  shipping  lots  may  be  twenty  to  thirty  pounds 
(9  to  14  kilos).  All  drillings  must  be  ground  and  mixed  before 
division.  The  grinding  is  done  in  a  mill  with  slightly  corrugated 
or  toothed  plates.  The  movable  plate  revolves  horizontally 
against  the  fixed  plate.  They  may  be  of  good  cast  iron,  but 
chrome  steel  is  better,  although  it  is  difficult  to  get  good  castings 
of  this  material  and  inequalities  cannot  be  adjusted  by  machining. 

All  the  drillings  should  be  ground  to  pass  a  screen  with  8 
meshes  to  the  linear  inch,  and  then  thoroughly  mixed  and  divided 


28  ANALYSIS  OF  COPPER 

on  a  riffle,  or  split  sampler,  to  obtain  a  sample  of  seven  or  eight 
pounds  (3.2  to  3.7  kilos).  This  sample  should  be  ground  re- 
peatedly, until  all  particles  pass  at  least  a  16-mesh  screen.  A 
fineness  of  20  mesh  is  preferable  and  drillings  may  easily  be  ground 
to  this  fineness  if  they  are  thin  enough  originally.  The  finely 
ground  drillings  should  be  thoroughly  mixed  and  divided  with  a 
split  sampler  or  riffle  into  the  required  number  of  packages.  No 
attempt  should  be  made  to  dip  with  a  spatula,  or  to  quarter  the 
ground  borings,  but  the  greatest  care  must  be  used  to  include 
the  proper  proportion  of  fine  and  coarse  in  each  package. 

If  much  gold  and  silver  are  present  and  there  is  a  large  differ- 
ence between  the  assay  values  of  the  fine  and  coarse  parts  of  the 
ground  sample,  the  whole  of  the  16-  or  20-mesh  sample  should  be 
weighed  and  separated  into  fines  and  coarse  on  a  screen  of  40 
meshes  to  the  linear  inch.  The  fines  should  be  weighed  and  the 
finished  samples  should  include  separate  parcels  of  the  coarse 
and  the  fine  parts  together  with  a  memorandum  of  weights  and 
their  mutual  ratio. 

22.  Method  of  F.  Andrews.  —  The  principle  given  is  the  same 
as  the  one  first  quoted.     This  system  provides  for  material  of 
variable  composition. 

From  20  to  100  per  cent  of  the  lot  is  sampled  by  drilling  a  J- 
inch  hole  through  each  sample  piece,  and  in  rotation  as  already 
directed.  The  templates  are  of  the  exact  size  of  the  surface  to  be 
covered,  and  each  brand  of  material  has,  of  course,  its  own  inde- 
pendent template.  The  drillings  are  ground  twice  and  then  cut 
down  by  a  divider  to  four  or  five  pounds.  This  amount  is  then 
further  ground  until  it  all  passes  through  a  16-mesh  sieve.  The 
whole  sample  is  then  put  through  a  40-mesh  sieve,  the  coarse  and 
fines  weighed,  and  the  required  number  of  samples  put  up  with 
proportionate  parts  of  coarse  and  fines  in  separate  bags. 

Each  sample  then  comes  to  the  laboratory  composed  of  two 
parts,  one  (coarse)  which  has  remained  on  the  40-mesh  sieve  and 
the  other  (fine)  which  has  passed  through.  In  weighing  up  for 
the  gold-silver  assay,  the  assay  ton  is  made  up  of  proportionate 
parts  of  coarse  and  fines,  but  the  copper  assay  is  made  on  each 
part  separately,  5-gram  portions  being  used  and  the  correct  assay 
figured  from  the  proper  weights. 

23.  Method  of  F.  D.  Greenwood  (for  uniform  material).  — • 
It  is  recommended  that  the  ground  borings  should  be  directly  cut 


SAMPLING  AND  CRUSHING  29 

down  on  a  split  sampler  in  such  a  way  as  to  obtain  a  sample  of 
about  1  assay  ton  (29.167  grams)  for  the  gold  or  silver  assay. 
For  the  copper  assay  of  crude  oullion,  80  grams  are  taken,  and  in 
each  case  the  final  sample  must  Include  the  proper  proportion  of 
the  finer  and  coarser  parts  of  the  borings. 

This  sample  must  be  very  carefully  obtained  for  reasons 
already  stated.  Portions  "dipped"  from  the  sample  bottle  or 
from  the  sample  spread  out  on  paper,  are  likely  to  contain  undue 
amounts  of  coarse  or  fine. 

24.  Metallic  Iron  in  Drillings  (A.  M.  Smoot).  —  There  is  a 
very  small  amount  of  iron  introduced  in  the  drilling  and  grinding 
of  converter  and  blister  copper,  but  it  is  wrong  to  attempt  to 
remove  it  from  the  ground  borings  by  a  magnet,  because  crude 
copper  always  contains  magnetic  particles,  due  to  matte,  etc., 
which  properly  belong  to  the  sample.     Any  attempt  to  remove 
such  iron  with  a  magnet  will  introduce  a  larger  error  than  it  will 
cure.     Practically,  the  amount  of  iron  derived  from  the  tools  is 
negligible,  since  ground  turnings  seldom  contain  more  than  .03 
per  cent,  and  a  large  part  of  this  is  present  in  the  original  copper. 

Iron  due  to  the  tools  may  be  separated  in  part  by  treating  the 
original  turnings  with  a  magnet  and  carefully  saving  the  magnetic 
particles.  After  grinding  in  the  mill  and  dividing  by  riffle  to  the 
amount  required  for  the  sample  packages,  go  over  the  drillings 
again  with  a  magnet  and  discard  any  magnetic  particles  obtained. 
Restore  to  the  sample  a  proportionate  part  of  the  magnetic  par- 
ticles originally  found  in  the  whole  sample  and  mix  thoroughly. 

25.  Moisture  in  Converter  and  Blister  Copper.  —  The  rough 
surface  of  such  metal  contains  many  cavities  which  may  retain 
appreciable  moisture  if  the  copper  has  been  exposed  to  the  weather. 
This  is  apt  to  occur  in  winter  when  bars  have  been  stored  in 
yards  exposed  to  snow,  or  shipped  without  protective  covering. 
The  per  cent  of  superficial  moisture  is,  of  course,  very  small,  and 
the   average   amount   may   be   easily   ascertained   by   moderate 
drying. 

Bosh-cooled  crude  copper  nearly  always  contains  " occluded" 
water  held  in  large  cavities  under  the  rough  surfaces  which  could 
not  be  affected  by  weather.  The  " occluded  moisture"  may  in 
some  cases  amount  to  0.1  per  cent  or  even  0.2  per  cent  by  weight. 
This  moisture  is  difficult  to  remove.  Long  continued  drying  at  a 
temperature  of  about  350°  F.  is  necessary.  Of  course,  such 


30  ANALYSIS  OF  ^COPPER 

moisture  is  unevenly  distributed,  and  a  large  number  of  bars  must 
be  dried  to  secure  even  reasonable  accuracy.  This  necessitates  a 
special  drying  chamber. 

SAMPLING    OF    REFINED    WIRE-BARS,    CAKES,    AND    INGOTS 

26.  The  method  specified  by  the  American  Society  for  Testing 
Materials  in  the  year  1913,  for  drilling  cast  metal,  involves  the 
driving  of  several  holes  clear  through  the  casting  in  three  direc- 
tions, from  top,  side,  and  bottom,  after  removing  and  rejecting 
the  surface  oxide  from  the  space  drilled. 

F.  D.  Greenwood,  and  others,  drill  the  holes  J  inch  to  \  inch 
deep,  rejecting  the  drillings,  then  drill  in  the  same  holes  until 
the  drill  is  within  J  inch  from  the  bottom.  The  drillings  are  cut 
up  with  snips  and  only  clean  bright  drillings  are  accepted. 

The  author  drills  two  holes,  at  least,  in  the  top,  side,  and 
bottom,  with  the  precautions  specified,  but  only  halfway  through, 
which  gives  practically  the  same  sample  but  causes  less  heating 
and  danger  of  oxidation.  All  borings  must  be  tested  with  a  magnet 
and  freed  from  dirt  by  sifting  through  a  40-mesh  sieve,  then 
placed  in  clean  dry  bottles,  as  they  oxidize  rapidly  if  stored,  or 
shipped,  in  envelopes.  Flat  anodes  or  sample  plates  are  drilled 
through,  including  the  oxide,  as  indicated  under  "The  sampling 
of  molten  copper  at  furnaces." 

SAMPLING    OF    COAL    AT    SMELTING    WORKS 

A  special  system  is  recommended  for  the  sampling  of  cars 
and  cargoes.  The  methods  of  subsequent  reduction  are  those 
proposed  by  a  joint  committee  of  the  American  Society  for  Test- 
ing Materials  and  the  American  Chemical  Society,  and  published 
jointly  during  1914. 

27.  Shipment  of  Samples.  —  If  samples  are  shipped  from  a 
distance,  much  moisture  will  be  lost  unless  the  containers  are 
sealed.     When   the   moisture   content  is  important,   the   sample 
should  be  broken  to  half -inch  size  as  accumulated,  the  mixing 
done  quickly,  and  the  sample  transferred  to  a  glass  fruit  jar  or 
tin  with  screw  cap,  which  may  be  made  air-tight  by  sealing  with 
adhesive  rubber  tape    and    gaskets.     Three   pounds  is  a  usual 
sample  for  long-distance  shipment. 

28.  Car    Sampling.  —  The    1899    Coal    Committee  l    recom- 
1  /.  Am.  Chcm.  Soc.  (1899),  1116.     Sec  also  "Coal,"  by  Sommermeier. 


SAMPLING  AND  CRUSHING  31 

mended  that  the  sampler  should  take  a  sample  of  six  scoop  shovels 
at  regular  intervals  on  each  side  of  the  car.  '  The  shovel  should 
be  brought  out  full.  Spread  ou  a  tight  floor  and  break  all  lumps 
larger  than  an  orange.  Shovel,  quarter,  break  finer  (in  a  power 
crusher  if  possible),  ancf  quarter  or  riffle  until  the  sample  is  re- 
duced to  3  pounds.  Manipulate  quickly  and  transfer  to  a  large 
fruit  jar.  A  carload  of  such  material  as  lignite  may  lose  several 
hundred  pounds  in  transit,  and  the  U.  S.  Geological  Survey  has 
proved  that  during  a  150-mile  haul,  there  is  a  decided  tendency 
for  slate  to  settle.  In  such  a  case,  sample  the  whole  face  of 
the  load  at  the  middle  and  ends  of  the  car,  while  unloading. 

According  to  A.  D.  Little,  the  ratio  of  the  largest  pieces  of 
coal  to  the  total  weight  of  sample  at  each  stage  of  the  reduction 
process  should  be  less  than  0.01  per  cent,  if  errors  of  1  per  cent  in 
the  ash  determination  are  not  to  be  exceeded  in  a  single  sampling 
of  a  fuel  containing  5  per  cent  of  ash.  N.  W.  Lord  insists  that  this 
ratio  should  be  that  of  the  maximum  slate  sizes  to  the  total  sample, 
which  is  a  good  proviso  for  very  low-grade  fuel.1 

29.  Vessel  Cargoes.  —  To  sample  coal  on  a  very  large  scale, 
as  unloaded  by  several  power  hoists,  the  system  adopted  by  the 
Calumet  &  Hecla  Mining  Co.  is  recommended.  A  large  covered 
barrel  of  corrugated  galvanized  iron  is  placed  beside  the  scales  on 
the  elevated  platform  of  each  hoist.  The  buckets  of  coal  are 
dumped  on  a  grizzly,  or  coarse  screen,  from  which  the  clean  lump 
coal  flows  to  the  gravity  distributing  car.  The  weigher  grabs  a 
piece  of  coal  (without  selection)  from  one  car  out  of  five,  or  in 
such  proportion  that  the  total  sample  shall  be  about  one  part  in 
five  thousand. 

The  fine  coal  slides  beneath  the  hoist  down  a  closed  chute, 
from  which  it  is  drawn  into  railroad  cars  and  sent  to  boilers  for 
immediate  consumption.  The  fines  are  separately  weighed, 
sampled,  and  analyzed.  The  analysis  of  the  whole  cargo  is  then 
calculated  from  the  tests  of  the  lump  coal,  A,  and  the  fines,  B, 
according  to  their  actual  relative  weights.  By  storing  only  clean 
lump  coal,  the  danger  from  spontaneous  combustion  is  minimized, 
and  a  better  knowledge  of  the  composition  is  obtained  than  by 
any  attempt  to  estimate  the  proportions  of  coarse  and  fines. 
If  such  an  elaborate  sj^stem  is  out  of  the  question,  a  small  propor- 
tion of  the  total  load  may  be  dumped  separately  and  shoveled 

1  Bailey  and  Brady,  /.  Ind.  and  Eng.  Chem.  1, 161,  263,  316.     Ibid.  6,  517. 


32  ANALYSIS  OF  COPPER  ' 

over   an  inclined  screen,  and  the  parts  separately  weighed,  to 
obtain  a  practical  estimate. 

30.  Reduction  of  Lump  Coal  for  Assay.  —  The  car,  or  cargo, 
sample  is  run  through  a  large  jaw  crusher  to  1.5-inch  size,  and 
rapidly  reduced  by  coning  and  half -shoveling  to  50  or  75  pounds. 
This  is  now  to  be  reduced  to  a  2-  to  5-pound  sample  for  assay.    If 
the  laboratory  is  near  at  hand,  the  whole  sample  is  transferred  in 
iron  pails,  and,  if  very  moist,  is  broken  to  J-inch  size  and  dried  at 
a  low  heat  in  iron  pans  (moisture  1).      If  fairly  dry,  the  sample 
is  broken  down  at  once  to  pass  a  sieve  of  4  meshes  to  the  linear 
inch  and  quartered  to  3  or  5  pounds  before  drying.     Samples  are 
preserved  in  tight  fruit  jars  with  screw  caps,  as  already  described, 
if  the  preliminary  reduction  must  be  made  at  some  distance  from 
laboratories.     If  a  sample  of  3  to  5  pounds  is  dried  at  15°  C. 
above    room    temperature,    Appalachian    bituminous    coal    and 
anthracite  will  be  air-dry  if  placed  in  the  drier  in  circulating  air 
over  night.     Illinois  coals  may  require  48  hours  and  lignites  72 
hours  for  the  preliminary  air-drying. 

31.  Reduction   to   Assay   Sample.  —  Immediately   after   the 
last  weighing,  the  entire  dried  portion  should  be  rapidly  pulverized 
to  10-mesh  size;    mixed  and  reduced  to  450-500  grams  with  an 
inclosed  riffle  sampler  having  J-inch  divisions.     If  reduction  is 
carried  directly  to  60-mesh  fineness,  there  will  be  loss  of  moisture. 
With  ordinary  open  grinders,  the  author  finds  it  most  accurate 
to  grind  quickly  through  a  20-mesh  sieve,  then  dry  over  steam 
plate,  or  in  an  oven  below  100°  C.,  for  1|  hours  (giving  moisture 
per  cent  No.  2) .     100  grams  is  afterward  reduced  to  pass  a  sieve 
of  60  meshes  to  the  linear  inch  (25  per  cm.). 

The  Official  Committees  (35)  recommend  that  the  500-gram 
sample  be  ground  directly  to  60  mesh  in  a  closed  porcelain  Abbe 
ball  mill  at  60  revolutions  per  minute.  Bituminous  coals  require 
1  hour's  time  and  anthracites  2  hours'.  The  jar  should  contain 
about  one-third  its  volume  of  1-inch  well-rounded  pebbles.  The 
best  machine  for  the  grinding  of  3-  to  5-pound  samples  to  10  or  20 
mesh  is  an  inclosed  coffee  mill  or  a  Hance  Bros.  &  White  drug 
mill  with  corrugated  plates,  and  fitted  with  pulleys.  In  the 
analysis  of  the  fines  another  moisture  test  is  often  made  by  drying 
one  hour  at  100-110°  C.  Neither  the  grinding,  or  drying,  of 
coals  should  be  carried  too  far,  and  uniform  conditions  must  be 
maintained  to  obtain  satisfactory  results.  The  latest  modifica- 


SAMPLING  AND  CRUSHING  33 

tions  of  standard  methods  of  analysis  are  found  in  the  reports  of 
coal  committees;  for  which  see  reference  (35)  at  the  close  of  this 
chapter.  > 

GOLD    AND    SILVER    BULLION 

32.  Method  of  U.  S.  Mint.  —  The  following  description  is 
based  on  a  paper  of  F.  P.  Dewey  and  the  practice  of  refinery 
chemists,  who  follow,  quite  closely,  the  Mint  method.  In  the 
purchase  of  bullion  by  the  Mint  the  size  of  the  deposit  has  an 
important  bearing  on  the  sampling.  When  the  weight  of  a  deposit 
reaches  300  ounces  Troy,  the  samples  become  important,  and 
with  bars  weighing  700-1200  ounces,  correct  work  is  essential. 
High-grade  bullion  and  coin  gold  do  not  segregate,  but  when  we 
come  to  consider  bullion  of  more  complex  composition,  the  matter 
assumes  greater  importance.  It  is  safe  to  assume  that  a  " brittle" 
bar  of  gold  bullion  will  not  be  homogeneous.  According  to 
Dewey,  there  is  only  one  satisfactory  method  of  sampling  of 
general  gold  bullions. 

(a)  "Dip"  samples  are  taken  by  pouring  a  small  portion  of 
the  well-mixed  molten  metal  into  water  so  as  to  produce  globules 
or  granulations.  Granulations  are  sometimes  made  by  pouring 
directly  out  of  the  black-lead  crucible  into  water,  the  operation 
of  casting  being  interrupted  for  the  purpose.  A  good  sample  of 
silver  bullion  is  obtained  from  a  silver  refining  furnace  by  taking  a 
small  "dip  sample"  directly  from  the  metal  bath  after  every 
second  (1000-ounce)  bar  cast.  The  granulations  may  then  be 
mixed  and  reduced  in  size  by  shears,  if  necessary,  or  remelted. 

(6)  "Chips."  —  There  are  various  cases  where  a  bar  of  solid 
bullion  can  be  satisfactorily  tested  without  melting  by  cutting  a 
chip  with  a  chisel,  preferably  of  special  design.  Power-driven 
punches  may  be  used  and  machines  are  also  in  use  which  take 
out  a  triangular  piece  of  metal  by  means  of  a  projection  on  a 
lever  operated  by  a  cam.  The  chips  must  be  taken  from  a  corner 
or  along  the  edge  of  a  bar.  In  systematic  sampling  of  large  bars, 
two  chips  are  generally  cut,  one  from  the  top  and  one  from  the 
bottom  of  the  bar,  and  are  properly  identified. 

(c)  Drill  samples  are  taken  according  to  fixed  system,  but,  in 
large  bars,  there  is  a  wide  choice  in  the  location  of  holes.  A 
common  practice  in  the  Mint  service  is  to  drill  halfway  through 
at  diagonally  opposite  corners  of  the  top  and  unite  the  drillings 
for  the  top  sample.  The  remaining  corners  are  drilled  halfway 


34  ANALYSIS  OF  COPPER 

through  from  the  bottom,  and  the  drillings  mixed  for  the  bottom 
assay.  Occasionally,  with  large  bars,  the  four  drillings  are  kept 
separate,  and  sometimes  holes  are  drilled  near  the  center  of  the 
bars,  also. 

Drill  samples  are  often  better  than  chips,  especially  where 
large,  fairly  uniform  bars  are  sampled  by  a  well-designed  plan. 
Drill  samples  of  brittle  bars  are,  however,  liable  to  be  inaccurate 
because  of  difference  between  the  coarse  and  fine  parts,  although 
on  high-grade  gold  the  difference  may  be  as  low  as  .0001  between 
the  top  and  bottom. 

F.  P.  Dewey  concludes  that,  in  sampling  bars  of  gold  weighing 
over  300  ounces,  when  the  assayer  is  acquainted  with  the  bullion, 
he  may  accept  either  a  chip  or  drill  sample.  On  an  unknown  bul- 
lion, it  is  unsafe  to  accept  anything  but  a  properly  prepared  dip 
sample.  Some  metal,  such  as  " cyanide"  bullion  from  the  cyanide 
process,  must  be  refined  before  the  gold  can  be  accurately 
determined. 

33.  Special  Methods  of  Refineries.  —  An  easy  practical  way 
of  sampling  silver  bullion  at  furnaces,  while  casting,  has  been 
described  under  the  title  of  "dip  samples."     Dr.  E.  Keller,  in 
discussion  of  the  Mint  system,   suggested  that  the  thin  plate 
method  used  successfully  at  anode  furnaces  for  copper,  might 
also  be  applied  to  silver  bullion. 

H.  D.  Greenwood  uses  such  a  method,  casting  Dore  bullion 
into  (18  x  7  x  f  inch)  plates,  which  are  drilled  with  sVirich  holes 
on  the  checker-board  plan.  The  drillings  are  then  ground  to 
pass  30  mesh,  or  a  sieve  of  12  holes  per  cm.  Any  iron  is  removed 
from  samples  with  an  electro-magnet. 

STANDARD    METHOD    FOR    ZINC    SPELTER 

34.  Virgin  Spelter,  that   is,  spelter  made   from  ore   or  raw 
concentrates  by  process  of   reduction    and   distillation  and  not 
produced  from  reworked  metal,  is  considered  in  four  grades  by 
the  American  Society  for  Testing  Materials  (36),  and  by  the  sub- 
committee on   alloys  of  the  American   Chemical  Society   (37). 
For  the  methods  of  analysis  and  the  composition  of  each  grade, 
refer  to  methods  31-35,  Chapter  XIV. 

With  the  exception  of  two  or  three  minor  details,  the  same 
procedure  is  followed  by  each  Committee  in  the  sampling  of  zinc 
spelter. 


SAMPLING  AND  CRUSHING  35 

Ten  slabs  are  taken  at  random  from  each  carload,  or  lot, 
received.  The  first  authority  permits  a  smaller  sample  to  be 
taken  for  smaller  lots,  but  in  rio  case  less  than  three  slabs.  In 
case  of  dispute,  half  of  the  sample  is  to  be  taken  by  the  maker 
and  half  by  the  purchaser;  and  the  whole  shall  then  be  mixed. 

The  slabs  taken  as  a  sample  are  to  be  sawed  completely  across 
and  the  sawdust  used  as  a  sample.  In  case  no  saw  is  available, 
the  slabs  should  be  drilled  completely  through  and  the  drillings  cut 
up  into  short  lengths.  The  Committee  of  the  American  Chemical 
Society  recommend  that  three  9-mm.  holes  should  be  drilled  along 
one  diagonal  of  each  slab.  One  hole  should  be  drilled  as  nearly 
as  possible  at  the  middle  and  the  others  halfway  from  the  middle 
toward  each  end  of  the  diagonal  line. 

No  lubricant  is  permitted  in  either  sawing  or  drilling.  The 
saw  or  drill  must  be  thoroughly  cleaned,  and  the  sawdust  or 
drilling  must  be  carefully  treated  with  a  magnet  to  remove  any 
particles  of  iron  derived  from  the  tools. 


36 


ANALYSIS  OF  COPPER 
LITERATURE  OF  SAMPLING 


Name 

Subject 

Reference 

1.  D.  W.  Brunton  .... 

Mine  sampling  

Trans.  A.  I.  M.  E.  25,  826. 

2.  (a)  S.  A.  Reed  .  . 

Theory  of  sampling 

Ibid.  40,  567. 
School  of  M  Quarterly  1885 

(6)  E.  Keller  

Pig  copper  sampling 

Trans    A    I    M    E  27,  106 

(c)     "      "     

Mattes.  . 

Mineral  Industry  10,  242 

(d)     "     "      

Mathematics  of 

Eng.  and  Min  J    93,  703 

(e)  D.  M.  Liddell  .  . 
(/)  A.  M.  Smoot.  .  . 

(I                        U 

((               « 

Ibid.  90,  897. 
Ibid.  93,  1213. 

3.  Edmund  Kirby  .... 

Mine  sampling  

Ibid.  69,  196-247. 

4.  J.  A.  Church 

Machines 

Ibid  86,  291  338 

5.  T.  A.  Rickard  

Mines  

Ibid.  76,  213-305. 

6.  Philip  Argall  

Mines 

Ibid  76,  888 

7.  G.  D.  Bancroft  .... 

Mines.    .    . 

Ibid  75,  323 

8.  E.  E.  White  

Drill  holes 

Proc.  Lake  Sup  Min  Inst  16, 

9.  W.J.Adams.. 
10.  Wm.  Wraith 

Ore  shipments  
JVlolten  copper  anodes 

100. 
MiningSci.  Press,  1904,  Aug.  6. 
Trans  A  I  M  E  41  318 

11.  E.Keller  
12.  E.  A.  Hersam 

(i            it            u 
Sizes  of  Screens 

Ibid.  42,  905. 
Ibid  37,  265 

13.  R.  H.  Richards  
14.  Whitehead  &  Ulke  . 
15.  F.  P.  Dewey.  .  . 

Screen  standards  
Gold  bullion  
Gold  bullion  at  Mints 

Ore  Dressing,  3,  1103. 
Eng.  &  Min.  J.  66k,  189. 
Trans.  A.  I    M    E    43,  870 

16.  John  Jewett  
17.  Bailey  &  Brady  
18.  G.  C.  Stone  

Smelter  deductions  .  .  . 
Accuracy  with  coal  .  .  . 

1075. 
Eng.  &  Min.  J.  73,  217. 
J.  Ind.  &  Eng.  Chem.  1,  161. 
Ibid.  1,  262. 

19.  E.  P.  Mathewson.  .  . 
20 

Sampling  Mills 
Anaconda 

Eng.  &  Min.  J.  86,  338. 
Ibid.  82,  624. 
Ibid.  82,  1165. 
Ibid.  81,  509. 
Mineral  Industry,  16,  300. 
Ibid.  14,  164. 
Ibid.  10,  206 
Eng.  &  Min.  J.,  90,  1059. 
Ibid.  82,  257. 
Ibid.  82,  261. 

Eng.  &  Min.  J.  83,  232. 
Ore  Dressing,  2,  844,  1570. 
Eng.  &  Min.  J.  70,  549. 
Ibid.  71,  534. 
Ibid.  76,  729. 
Proc.  Am.  Soc.  Test.  Materi- 
als, XIII. 

Proc.   Am.   Soc.   Test.   Mat. 
XIV,  409. 
J.  Ind.  &  Eng.  Chem.  6,  517. 

Am.  Soc.  Test.  Materials 
Year  Book,  1914,  284. 
J.  Ind.  &  Eng.  Chem.  7,  547 
(1915). 

Greene  Cananea  
Cobalt,  Ont. 

21.  F.  F.  Colcord  

22.     . 

Garfield,  Utah  
U.S.  Metals  Co  
Michigan  Smelter.  .  .  . 
B.  C.  Copper  Co  
Tooele  Utah 

23.  .. 

24.  .. 

25.  Paul  Johnson 

26.  Repath  &  McGregor 
27  

Copper  Queen  
Britannia  Co.,  B.  C..  . 

Laboratory  Machines 
Design  of  riffles  
Riffles  &  samplers  .... 
Lab.  sampler  

28  

29.  Haultain  
30.  R.  H.  Richards  
31.  Snyder  

32.  Calkins  

«          « 

33.  Jones  

"     riffle  sampler.  .  .  . 
Lab.  screens,  ratio.  .  .  . 

Sampling  of  Coal 

Report,  1914  
Of  Amer.  Chem.  Soc.  . 
"  Coal  Analysis"  

Zinc  Spelter 
Specification  

34.  G.  A.  Disbro  

35.  Committee,  E-4, 
1914  .. 

Joint  Committee  .... 
E.  Sommermeier.  .  .  . 

36.  Committee  Report  . 
37.  Sub-committee  

Approved  Report  

CHAPTER  III 
REAGENTS   AND    STANDARD    SOLUTIONS 

Introduction.  —  The  following  paragraphs  treat  of  the  impuri- 
ties in  chemical  reagents  which  may  injuriously  affect  the  accuracy 
of  the  analysis  of  copper.  The  fact  that  less  than  .0050  per  cent 
of  the  usual  impurities  is  required  to  affect  the  physical  proper- 
ties of  refined  copper,  together  with  the  demand  of  consumers  for 
metal  of  very  high  purity  and  of  strictly  uniform  quality,  make  it 
necessary  to  employ  for  such  tests  the  purest  chemicals  and  to 
make  blank  analyses  of  such  reagents.  The  chemist  of  the 
Wallaroo  Company  has  found  it  necessary  to  redistil  all  imported 
English  acids.  All  acids  mentioned  in  succeeding  chapters  should 
be  understood  to  be  of  the  purest  commercial  grade  obtainable 
and  of  the  maximum  strengths  given  below,  unless  dilute  reagents 
are  locally  specified. 

Definition  of  Density.  —  "Specific  Gravity"  is  a  longer  term 
than  the  one  of  " Density"  lately  recommended  by  the  U.  S. 
Bureau  of  Standards.  The  author  prefers  to  adopt  the  latter 
term  for  the  sake  of  brevity.  Density  is  defined  as  the  weight  in 
grams  of  a  cubic  centimeter,  or  as  the  ratio  between  the  weight  of 
a  substance  at  a  fixed  temperature  (15°  or  20°  Centigrade)  and  the 
weight  of  an  equal  volume  of  water  measured  at  4°  Centigrade, 
its  point  of  greatest  density. 

COMMERCIALLY    PURE    REAGENTS 

The  formulas  for  the  most  important  solutions  have  been 
arranged  in  a  regular  alphabetical  order  and  by  number.  Such  a 
system  is  easily  added  to  or  interpolated  and  permits  immediate 
reference  to  the  formula  if  the  numbers  are  also  placed  on  the 
corresponding  stock  bottles. 

Hydrochloric  acid,  HC1  (density,  1.18  to  1.20),  usually  contains 
a  trace  of  iron  and  arsenic.  The  product  of  the  electrolytic 
process  is  to  be  preferred  for  all  arsenic  and  antimony  distillations 
as  it  is  strictly  pure. 


38  ANALYSIS  OF  COPPER 

Nitric  acid,  HNO3  (d.,  1.42),  should  be  free  from  every  trace  of 
chlorine  and  nitrous  acid  when  used  for  electrolysis  or  gold  assay- 
ing. The  red-fuming  acid  for  oxidation  of  sulphides  should  have 
a  density  of  1.60  at  least. 

Sulphuric  acid,  H2SO4  (d.,  1.83-1.84),  often  contains  a  trace  of 
arsenic.  Some  of  the  high-grade  product  shows  a  trace  of  man- 
ganese, which  becomes  noticeable  in  the  determination  of  iron 
and  nickel  in  refined  copper. 

Ammonium  Hydroxide,  NH4OH  (d.,  .90),  unless  of  extreme 
purity,  will  show  injurious  amounts  of  iron  in  addition  to  the 
usual  traces  of  pyridine.  Not  more  than  .0001  per  cent  of  the 
latter  should  be,  present  in  ammonia  used  for  the  separation  of 
arsenic  or  antimony  from  copper  by  precipitation  with  excess  of 
ferric  salts. 

PREPARATION    OF    PURE    GASES  —  CARBON    MONOXIDE 

Carbon  Monoxide,  CO,  may  be  prepared  by  dropping  strong 
sulphuric  acid  into  98  per  cent  formic  acid.1  The  acid  is  placed 
in  a  small  flask,  and  the  gas  must  be  purified  from  a  little  carbon 
dioxide  by  passing  it  through  potassium  hydroxide  solution, 
then  through  alkaline  pyrogallate  of  potassium  to  remove  traces' 
of  oxygen,  and  finally  through  drying  tubes. 

To  secure  an  even  flow  of  gas,  raise  the  temperature  of  the 
flask. 

CARBON    DIOXIDE 

Carbon  dioxide,  COz,  may  be  obtained  in  a  very  pure  state  by 
dropping  strong  sulphuric  acid  into  a  flask  half  filled  with  a  thick 
paste  of  sodium  bicarbonate  and  water,  as  recommended  by 
Bradley  and  Hale.2 

This  method  is  inconvenient  for  analytical  purposes.  Gas 
of  sufficient  purity  for  use  in  the  "Determination  of  oxygen  in 
copper"  (Chapter  XIII)  is  generated  by  the  action  of  dilute 
hydrochloric  acid  on  lumps  of  white  marble.  The  traces  of 
oxygen  present  are  absorbed  by  passing  the  gas  through  a  15-cm. 
roll  of  red-hot  copper  gauze,  contained  in  a  25-cm.  ignition  tube. 
To  avoid  rapid  deterioration  of  the  copper,  the  burner  should  not 
be  lighted  until  the  air  has  all  been  driven  out  of  the  bottle  and 
tubes.  The  coil  is  easily  regenerated  by  reversing  the  valves, 
opening  a  stopper  in  the  rear  of  the  tube,  and  passing  hydrogen 

1  E.  Rupp,  Chem.  Ztg.  32,  983.  2  J.  Am.  Chem.  Soc.  30,  1090. 


REAGENTS  AND  STANDARD  SOLUTIONS  39 

gas  from  a  second  generator  for  15  minutes.  The  purification 
train  of  tubes  may  be  arranged- in  order  thus:  (a)  Casamajor 
generator,  or  a  small  Kipp  with,  pressure  tube  above;  (b)  Bulb 
of  saturated  neutral  ^potassium  permanganate,  or  mercuric 
chloride,  for  absorption  of  hydrocarbons;  (c)  U-tube  of  silver 
sulphate;  (d)  Bo  wen's  potash  bulb  with  strong  sulphuric  acid; 
(e)  Tube  with  the  roll  of  copper  gauze;  (/)  Two  drying  tubes  of 
calcium  chloride,  sulphuric  acid,  or  phosphorous  pentoxide,  as 
preferred. 

HYDROGEN 

Hydrogen  gas  may  be  more  easily  purified  if  it  is  generated  by 
pure  zinc  and  dilute  sulphuric  acid  (not  hydrochloric  acid). 
A.  M.  Smoot  recommends  the  addition  of  one  drop  of  platinic 
chloride  solution  to  two  liters  of  (1:4)  acid.  The  purifying  train 
consists  of:  (a)  The  generator,  or  gas  cylinder;  (6)  Allihn 
washing  bottle  of  10  per  cent  potassium  hydroxide,  saturated  with 
potassium  permanganate;  (c)  Tubes  for  the  removal  of  traces  of 
oxygen.  Here  there  is  a  choice  of  at  least  three  alternatives, 
the  first  being  preferred,  —  (1)  Allihn  250  c.c.  bottle  of  potassium 
hydroxide  solution  (d.,  1.27)  in  which  is  dissolved  5  grams  of 
pyrogallic  acid;  (2)  a  heated  tube  of  5  per  cent  palladium 
asbestos;  (3)  a  tube  containing  a  long  roll  of  reduced  copper  gauze 
heated  by  a  short  furnace;  (d)  Finally,  two  tubes  of  drying 
agents,  as  described  under  "  Oxygen,"  Chapter  XIII. 

SULPHUR  DIOXIDE 

Sulphur  dioxide,  S02,  has  been  obtained  by  heating  turnings 
of  copper  with  sulphuric  acid.  Whenever  a  cylinder  of  the 
compressed  gas  is  not  at  hand,  the  easiest  method  of  generation 
consists  in  dropping  a  saturated  solution  of  sodium  sulphite 
from  a  separatory  funnel,  through  a  tube  of  soft  glass,  which 
dips  under  the  surface  of  400  to  500  c.c.  of  sulphuric  acid,  con- 
tained in  a  liter  flask. 

NOTE.  —  Oxygen,  O2,  simply  requires  a  purification  from 
traces  of  carbon  dioxide,  with  the  addition  of  drying  tubes,  un- 
less it  is  to  be  used  for  the  combustion  of  carbon.  In  that 
case,  a  heated  catalyzer  tube  should  precede  the  potassium 
hydroxide. 


40  ANALYSIS  OF  COPPER 

STANDARD   SOLUTIONS 

The  standard  solutions  are  numbered  as  a  means  of  ready 
reference,  and  are  those  employed  in  the  methods  described  in 
succeeding  chapters. 

Unless  otherwise  specified,  they  are  made  with  the  com- 
mercially pure  reagents,  sold  as  "  chemically  pure." 

1.  Acid  Mixture,  for  the  electrolytic  assay  of  copper  (method 
2,    Chapter  XI).     This   mixture,  which   has   been  adopted   by 
several  works,  permits  direct  electrolysis  without  any  evapora- 
tion,  as  soon  as  the   copper  drillings  are  dissolved   upon  the 
steam  plate  and  the  solution  diluted.     It  is  made  up  in  large 
quantities  in  the  following  proportions   by  volume:    7   parts   of 
nitric  acid  (d.,  1.42),  10  parts  of  sulphuric  acid  (d.,  1.84),  and 
25  parts  of  distilled  water,  strictly  free  from  chlorides. 

2.  Ammonium     Oxalate,     (NH4)2C2O4.H2O. —  A     saturated 
solution  is  used  for  the  precipitation  of  calcium,  or,  if  preferred, 
a  10  per  cent  solution  of  the  crystals.     10  c.c.  of  the  latter  pre- 
cipitates about  .4  gram  CaO. 

3.  Ammonium  Molybdate,   (NH4)6Mo7024.4H20,  is   required 
in  the  titration  of  lead  in  the  " Western  method"  for  ores  or 
slags  (Chapter  V).     Dissolve  4.3  grams  in  200  c.c.  of  water,  add 
a  few  drops  of  ammonia,  and  make  up  to  one  liter.     1  c.c.  is 
nearly  equivalent  to  .005  gram  of  lead  (Pb).     To  standardize, 
dissolve  .200  gram  of  chemically  pure  lead  foil  in  dilute  nitric 
acid.     Make  the  liquid  alkaline  with  ammonia,  boil  for  a  minute, 
then  render  the  solution  acid  with  acetic  acid  and  titrate.     Use 
a  solution  of  1  gram  of  tannin  in  300  c.c.  of  water  as  an  indicator. 
Deduct  the  amount  of  molybdate  required  to  affect  the  indicator 
from  the  total  amount  discharged  from  the  burette. 

4.  Ammonium  Molybdate  is  also  employed  as  an  indicator 
in  the   titration  of  zinc.     Prepare  a   1   per  cent  solution  with 
distilled  water. 

5.  Ammonium  Acetate,  (NH4C2H3O2),  is  used  as  a  saturated 
solution  in  the  extraction  of  lead  from  various  precipitates,  such 
as  silica,  or  barium  sulphate  (Chapter  V).     Glacial  acetic  acid 
may  be  very  slowly  added  to  concentrated  ammonium  hydroxide 
until  the  liquid  is  slightly  acid.     For  ordinary  work,  the  solution 
may  then  be  made  slightly  alkaline. 

6.  Ammonium  Phosphate,  Secondary,  (NH4)2HPO4,  may  be 


REAGENTS  AND  STANDARD  SOLUTIONS  41 

made  up  as  a  10  per  cent  solution  for  the  precipitation  of  mag- 
nesium. 1  c.c.  will  precipitate  about  .0305  gram  of  the  oxide, 
MgO.  The  same  reagent  is  employed  in  the  "  Phosphate 
method"  for  alumina,  described  in  Chapter  V. 

7.  Ammonium  Sulphydrate,  NH4HS,  must  be  frequently  pre- 
pared, as  it  does  not  keep  unaltered  many  days.     Saturate  strong 
ammonia,  free  from  pyridine,  with  pure  hydrogen  sulphide  until 
the  iron  is  precipitated  as  black  sulphide  and  the  supernatant 
liquid  is  yellow.    After  settling,  the  solution  should  be  filtered 
into  a  brown  glass-stoppered  bottle. 

8.  Ammonium  Thiocyanate,  NH4SCN,  is  required  as  a  pre- 
cipitant, and  also  as  a  standard  volumetric  solution.     In  method 
3,  Chapter  IV,  a  solution  of  40  grams  per  liter  is  adopted  as  a 
precipitant  of  copper  in  the  assay  of  copper  in  ores. 

9.  Ammonium  Thiocyanate  for  the  titration  of  silver  arsenate, 
in  method  12,  Chapter  V,  is  made  of  such  a  strength  that  1  c.c. 
equals  .001  or  .005  gram  of  arsenic.     It  is  standardized  against 
a  weighed  quantity  of  pure  silver  dissolved  in  nitric  acid.     107.88 
parts  of  silver  =  25  parts  of  arsenic. 

10.  For  method  7,  Chapter  IX,  the  thiocyanate,  or  sulpho- 
cyanate,  is  adopted  as  a  finishing  solution  in  the  refinery  method 
for  titration  of  silver  bullion,  following  a  standard  solution  of 
hydrochloric  acid  (19).     1  c.c.  equals  .001  gram  of  metallic  silver. 

11.  Ammonium  Thiocyanate,  as  a  precipitant  of  copper  in 
complete   analysis   of   the   metal,    is   prepared   by   dissolving    1 
pound,  or  453.6  grams,  of  the  crystals  in  2  liters  of  distilled 
water.     1  c.c.  will  precipitate  about  0.12  gram  of  copper  in  the 
presence  of  an  excess  of  sulphur  dioxide,  sufficient  to  saturate 
the  solution  and  complete  the  reduction  of  the  precipitate  to  the 
white  cuprous  thiocyanate. 

12.  Barium  Hydroxide,  Ba(OH)2,  is  employed  in  the  form  of 
a  saturated  solution  for  the  absorption  of  carbon  dioxide  in  steel 
analysis,  or  for  carbon,  etc.,  in  ores.     Stir  20  grams  of  the  hy- 
droxide in  1  liter  of  hot,  freshly  boiled  distilled  water,  and  after 
settling,  filter  quickly  through  a  covered  funnel  into  a  closed 
flask,  provided  with  a  rubber  stopper  perforated  for  two  tubes. 
Through  one  hole  is  passed  the  stem  of  a  100  c.c.  pipette,  and 
through  the  other,  a  short  bent  tube  of  soda  lime  to  protect 
the  liquid  from  the  carbon  dioxide  of  the  air.     For  each  analysis, 
90  to  100  c.c.  are  pipetted  into  a  straight  10-bulb  absorption  tube. 


42  ANALYSIS  OF  COPPER 

13.  Barium  Chloride,  BaCl2.2H2O.  —  A  solution  of  nearly  10 
per  cent  strength  is  used  as  a  precipitant  only. 

14.  Bismuth  Sulphate.  —  For  the  color  method  of  F.  B.  Stone, 
in  the  analysis  of  refined  copper  (7,  Chapter  XIII) .     Dissolve  the 
chemically  pure  metal,  or  oxide,  evaporate  with  a  slight  excess 
of  sulphuric  acid  until  any  other  acid  is  removed,  then  dilute 
until  1  c.c.  contains  .0001  gram  of  bismuth.     In  making  color 
tests,  a  little  sodium  sulphite  solution  is  added  to  decolorize  any 
trace  of  ferric  salt. 

15.  Cadmium  Chloride,  CdCl2,  in  an  ammoniacal  solution, 
absorbs  sulphur,  when  evolved  as  hydrogen  sulphide  from  metals. 
Dissolve  12.5  grams  of  the  choride  (according  to  J.  M.  Camp), 
in  125  c.c.  of  water,  add  100.  c.c.  of  ammonia  (d.,  .90),  and  filter. 
Then  dilute  to  1  liter. 

10  c.c.  are  taken  for  the  absorption  of  the  sulphur  from  5 
grams  of  steel,  and  about  5  c.c.  for  sulphur  evolved  during  the 
reduction  of  copper  by  hydrogen  (method  15,  Chapter  XIII). 

16.  Copper-Potassium  Chloride  is  used  as  a  solvent  of  steel, 
which  permits  the  separation  of  carbon.     It  is  prepared  by  dis- 
solving 1  pound,  or  453.6  grams,  of  the  green  crystals  in  1  liter 
of  distilled  water,  filtering  through  a  plug  of  ignited  asbestos, 
and  adding  50  c.c.  of  strong  hydrochloric  acid.     For  carbon  in 
nickel  alloys,   a  saturated  neutral  solution  is  adopted,   adding 
acid   to   each   analysis    (16,    Chapter  XIV).     The    tops   of  the 
bottles  should  be  protected  from  dust. 

17.  Cupric    Chloride,    CuCl2. 2H2O,   as    a    solution    of    300 
grams  of  crystals  in   1  liter  of  hydrochloric  acid  (d.,  1.20),  is 
combined  with  No.  58  to  make  a  distilling  solution  for  arsenic 
(method  10,  Chapter  V). 

18.  Ferric  Ammonium  Sulphate,  Fe2(NH4)2(S04)4.12  H2O,  as 
a  10  per  cent  solution,  is  added  to  copper  solutions  as  a  precipi- 
tant of  the  arsenic  group  of  metals.     Ferrous   ammonium   sul- 
phate is  much  used  to  standardize  permanganate,  but  the  results 
do  not  always  agree  with  metallic  iron.     A  special  solution,  No.  40, 
is  used  with  No.  39  for  manganese. 

19.  Hydrochloric  Acid,  HC1,  diluted  to  the  " normal"  solution 
(36.468  grams  of  HC1  per  liter)  is  run  against  soda  in  alkalimetry. 
»      For  method  7,  Chapter  IX,  a  solution  is  prepared  of  such  a 
strength  that   100  c.c.   precipitates  a  few  milligrams  less  than 
2000  milligrams  of  silver. 


REAGENTS  AND  STANDARD  SOLUTIONS  43 

20.  Standard  Iodine.    As  a  titrating  solution  for  arsenic  in 
ores  (Chapter  V),  dissolve  12.828  grams  of  pure  iodine  and  19 
grams  of  potassium  iodide  in '200  c.c.  of  water  and  dilute  to  1 
liter.     1  c.c.    nearly  equals  .005^gram  of  arsenious  oxide,  As4O6. 
To  standardize,   dissolve  .2    gram    of   pure   arsenious   oxide    in 
a  very  little  sodium  hydroxide. 

Dilute  to  300  c.c.,  make  acid  with  sulphuric  acid,  using  only 
one  or  two  drops  of  dilute  acid  in  excess,  as  determined  by  a 
floating  piece  of  litmus  paper.  Add  an  excess  (4  to  10  grams)  of 
sodium  bicarbonate,  then  3  c.c.  of  No.  56  starch  solution,  and 
titrate  cold  to  a  purplish  blue. 

21.  Iodine  Solution,  for  the  titration  of  arsenic  from  refined 
copper,  is  made  by  dissolving  3.5  grams  of  "reagent"  iodine  with 
7  grams  of  the  potassium  iodide  in  a  little  water  and  diluting  to 
1  liter.     Allow  to  stand  a  day  before  use.     1  c.c.  titrates  about 
.001  gram  of  arsenic,  and  about  .04  c.c.  is  required  to  produce 
the     end-point.     Standardize    with    .06     gram    of    the    purest 
(99.9  per  cent)  arsenious  oxide,  just  as  for  solution  20,  but  add 
five  drops  of  a  10  per  cent  solution  of  potassium  iodide  to  the 
arsenious  solution  immediately  after  the  starch.     The  iodide  is 
added  to  obtain  a  definite  end-point  and  an  immediate  formation 
of  iodide  of  starch  in  presence  of  very  small  amounts  of  arsenic. 
See  method  6d,  Chapter  XII. 

22.  Iodine   Solution  for  the  titration  of  hydrogen  sulphide 
(when  liberated  from  cadmium  sulphide  in  the  determination  of 
sulphur  in  steel,  or  of  oxygen  in  copper),  may  be  made  of  such 
strength  that  1   c.c.  equals  .0025  gram  of  sulphur.     To  obtain 
this  strength,   dissolve  2  grams  of  purest   " reagent"  iodine  in 
100  c.c.  of  water  with  5  grams  of  potassium  iodide  and  dilute  to 
1    liter.     For    very    exact   work,    the    iodine    solution    may  be 
made  by  Payne's  formula.  —  See  " Methods  of  Iron  Analysis," 
by  F.  C.  Phillips,  page  22. 

23.  Magnesium  Sulphate,  MgSO4.7  H2O,  is  used  in  the  form 
of  the  well-known  " magnesia  mixture"  for  the  precipitation  of 
arsenic  and  phosphoric  acids.     Magnesium  sulphate  is  better  than 
the  chloride  because  it  contains  only  one-fifth  as  much  calcium 
salt,  which  is  present  as  an  impurity.     Fresenius'  formula  gives 
good  results :  —  Dissolve  1  part  of  magnesium  sulphate  crystals, 
4  parts  of  ammonium  chloride,  and  4  parts  by  volume  of  am- 
monia water  (d.,  0.9)  in  8  parts  of  water.     Allow  impurities  to 


44  ANALYSIS  OF  COPPER 

settle  and  then  filter.  An  old  solution,  which  has  perceptibly 
attacked  the  glass,  should  be  rejected  unless  any  precipitated 
silica  is  deducted. 

24.  Magnesium  Chloride,  MgCl2.6H20,  for  the  separation  of 
phosphoric  acid  from  ores,  slags,  or  limestone  (Chapter  V),  may 
be  made  up  by  the  formula  of  A.  A.  Blair.     Dissolve  110  grams 
of   the    crystals   in    water   and    filter.     Dissolve   280   grams    of 
ammonium  chloride  in  water,  add  a  little  bromine  water,  and  a 
slight  excess  of  ammonium  hydroxide,  heat  nearly  to  boiling,  and 
then  filter.     Mix  the  two  liquids,  render  the  mixed  liquid  faintly 
alkaline,   dilute  to  2  liters,   shake  occasionally,   allow  to   stand 
two  or  three  days,  and  filter  a  portion  into  a  small  bottle  as 
required.     10  c.c.  precipitates  .15  gram  of  magnesium  oxide,  MgO. 

25.  Manganous   Sulphate,  MnSO4.4  H2O,  is   combined  with 
phosphoric  acid   to   make    a   titrating   solution   known    as   the 
Zimmerman-Reinhardt  mixture.     It  is  added  in  their  method  for 
the  titration   of  reduced  iron   by  potassium   permanganate,   in 
order  to  obtain  a  clear  end-point.     Dissolve  160  grams  of  the 
manganese  salt  and  dilute  to  1750  c.c.     Add  330  c.c.  of  strong 
phosphoric  acid    and   320    c.c.   of  concentrated    sulphuric    acid. 
10  to  20  c.c.  of  the  mixture  are  added  to   each   iron  solution 
after  reduction  of  the  iron  by  stannous  chloride  and  mercuric 
chloride.     The  preceding  is  the  improved  formula  of  Mixer  and 
Dubois. 

26.  Mercuric  Chloride,  HgCl2,  is  used  as  a   saturated  solu- 
tion. ,5  c.c.  are  added  to  a  solution  of  ferrous  iron  after  reduction 
by  stannous  chloride,  in  order  to  destroy  the  slight  excess  of  the 
latter,  which  should  not  be  more  than  one  or  two  drops. 

27.  Mercuric  Nitrate  is  used  for  the  amalgamation  of  copper 
borings  in  the  " assay  of  gold  in  copper"  (method  3,  Chapter  X). 
Twenty-five  grams  are  dissolved  in  one  liter.     A  saturated  solu- 
tion  of  the   sulphate  in   dilute   sulphuric   acid   is   even   better. 
Take  10  c.c.  of  the  nitrate,  or  25  c.c.  of  the  sulphate  for  each 
"assay  ton"  sample  of  copper. 

28.  Dimethyl  Glyoxime,  for  the    precipitation  of    nickel  in 
ammoniacal  solution,  is  dissolved  in  the  proportion  of  1  gram 
to  100  c.c.  of  ethyl  alcohol.  —  Used  in  method  3,  Chapter  XIII. 

29.  Nitroso-/3-Naphthol    is    employed   as    a    precipitant    for 
cobalt  and  for  the  separation  of  cobalt  from  nickel  (method  2, 
Chapter  XIII). 


REAGENTS  AND  STANDARD  SOLUTIONS  45 

Dissolve  the  salt  in  acetic  acid  of  50  per  cent  strength  until 
the  acid  is  saturated. 

30.  Potassium  Cyanide,  itCN,  for  the  titration  of  copper  in 
ores   and   mattes,    according   to'  "  western   methods."     Dissolve 
22.5  grams  in  water  and  make  up  to  one  liter.     Use  the  chemi- 
cally pure  salt.     1  c.c.  equals  .005  gram  of  copper.     Standardize 
it  with  matte,  or  ore,  in  which  the  copper  has  been  determined 
electrolytically. 

31.  Potassium  Cyanide,  for  the  titration  of  nickel  in  ores,  or 
mattes,  is  made  of  a  strength  of  24.5  grams  per  liter  and  stand- 
ardized against  pure  nickel,  and  diluted  so  that   1  c.c.  equals 
.005  gram  nickel  (method  1,  Chapter  VII). 

32.  Potassium     Ferrocyanide,     K4Fe(CN)6.3H2O.  —  For     a 
standard  solution,  to  be  used  in  the  titration  of  zinc  in  ores  and 
slags,  dissolve  21.63  grams  of  the  salt  with  7  grams  of  sodium 
sulphite  crystals  in  water  and   make   up  to    1    liter.     1  c.c.  is 
equivalent  to  nearly  .005  gram  of  zinc.     To  standardize,  dissolve 
.200  gram  of  chemically  pure  zinc,  or  freshly  ignited  chemically 
pure  zinc  oxide,  in  15  c.c.  of  hydrochloric  acid.     Add  7  grams  of 
ammonium  chloride.     Dilute  to  200  c.c.  with  boiling  water  and 
titrate,  using  a  solution  of  one  gram  of  ammonium  molybdate 
in  100  c.c.  of  water  for  an  indicator.     Deduct  amount  of  ferro- 
cyanide  required  to  affect  the  indicator  from  the  total  amount 
used  (methods  16  and  17,  Chapter  VII). 

33.  Potassium  Ferrocyanide,  as  a  standard  solution  for  the 
titration  of  zinc  in  brass  and  German  silver  (Chapter  XIV),  is 
prepared  as  follows:    Dissolve  80  grams  of  the  salt  in  2500  c.c. 
of  distilled  water,  and  allow  to  stand  at  least  six  weeks  before 
use,  to  obtain  a  permanent  solution.     To  standardize,  weigh  2 
grams  of  zinc,  dissolve  in  nitric  acid,  and  make  up  to  one  liter. 
Take  100  c.c.  (.2  gram)  zinc,  add  5  c.c.  nitric  acid,  3  c.c.  strong 
ferric  chloride  solution,  20  c.c.  of  saturated  citric  acid  solution, 
dilute,  and  make  distinctly  alkaline  with  ammonia.     The  final 
volume    should    be   250    c.c.     Boil    the   liquid    and    titrate   the 
boiling  solution.     Fill  pits  in  a  porcelain  test  plate  with  50  per 
cent  acetic  acid,  and  add  2  drops  of  zinc  solution  to  determine 
the  end-point  which  changes  from  greenish  to  clear  blue.     The 
correction  for  the  amount  necessary  to  reach  the  end-point  in  a 
solution  free  from  zinc,  must  be  made  by  each  operator,  and  is 
about     c.c. 


46  ANALYSIS  OF  COPPER 

34.  Potassium  Bichromate,  K2Cr2O7,  is  used  to  make  up  a 
standard  titrating  solution  for  iron  in  the  " Western  methods" 
for  ores  (Chapter  V). 

Dissolve  3.408  grams  in  water'  and  make  up  to  one  liter. 
1  c.c.  is  equal  to  approximately  .005  gram  of  ferrous  oxide,  FeO. 
With  4.39  grams  of  fused  salt  per  liter,  the  iron  value  is  about 
.005  gram  per  c.c.  To  standardize  in  terms  of  iron,  or  ferrous 
oxide,  dissolve  .2  gram  of  analyzed  iron  wire  in  10  c.c.  of  (1:1) 
hydrochloric  acid  with  the  addition  of  a  few  crystals  of  potassium 
chlorate  to  destroy  any  trace  of  organic  matter.  Or  1  gram  of 
pure  ferrous  ammonium  .sulphate  may  be  dissolved  in  100  c.c. 
of  hot  water  and  10  c.c.  of  the  hydrochloric  acid.  In  either 
case,  add  one  or  two  drops  of  stannous  chloride  in  excess 
of  the  amount  required  to  decolorize  the  liquid. 

Remove  this  excess  of  stannous  chloride  by  adding  5  c.c.  of 
a  saturated  solution  of  mercuric  chloride,  which  should  pro- 
duce a  white  (not  dark)  precipitate.  Cool  by  diluting  to  300 
c.c.  or  more  and  titrate.  Test  drops  of  the  liquid  on  a  por- 
celain tile  with  a  drop  of  potassium  ferricyanide. 

35.  Potassium    Hydroxide,    KOH.  —  A   normal  solution  is 
56.1  grams  per  liter.     Potash  (purified  by  alcohol)  should  not 
be  used  for  gas  analysis. 

36.  Potassium  Chromate,  as  adopted  in  the  Guess  method 
for  lead  in  ores,  or  mattes,  is  made  up  with   100  grams  of  the 
salt,  K2CrO4,  per  liter.     1  c.c.  precipitates  about  106  milligrams 
of  lead. 

37.  Potassium  Iodide,  KI,  in  the  form  of  a  10  per  cent  solu- 
tion, is  added  in  the  titration  of  arsenious  oxide  by  standard 
iodine  (No.  20)  in  order  to  have  the  ions  required  to  produce 
an  immediate  formation  of  the  iodide  of  starch  with  the  slightest 
excess  of  iodine,  even  when  the  solution  titrated  contains  but  a 
trace  of  arsenic.     Add  five  or  six  drops  after  the  solution  has 
been  made  alkaline  by  the  large  excess  of  sodium  bicarbonate. 
The  titration  is  described  in  detail  under  the  "Determination  of 
arsenic  in  refined  copper"  (method  6d,  Chapter  XII). 

38.  Potassium   Iodide,   KI,   is  also  employed   as  an  active 
reagent  for  the  titration  of  nickel  in  matte  (method  14,  Chapter 
VI).     40  grams  are  dissolved  in  1  liter. 

39.  Potassium  Permanganate,  KMnO4,  for  the  titration  of 
moderate  amounts  of  iron  in  solution,  is  made  up  of  such  a 


REAGENTS  AND  STANDARD  SOLUTIONS  47 

strength  that  1  c.c.  will  oxidize  about  .005  gram  of  iron.  To 
this  end,  dissolve  2.86  grams  in  water  and  dilute  to  1  liter. 
This  strength  may  be  doubled  for  iron  ores  or  any  rich  material. 
The  iron  (Fe)  value  of^  1  c.c.  multiplied  by  .2951  gives  the 
value  in  terms  of  manganese  (Mn.),  as  determined  by  Volhard's 
method.  The  solution  is  standardized  by  various  methods  in 
different  laboratories.  The  author  prefers  soft  iron  wire  of 
known  composition,  for  the  determination  of  the  iron  value. 
In  the  titration  of  small  amounts  of  manganese  in  copper  ores, 
the  value  in  terms  of  manganese  may  be  found  by  multiplying 
the  value  in  calcium  oxide,  CaO,  by  .5878. 

40.  Potassium  Permanganate,  for  the  titration  of  oxalate  of 
calcium,    obtained   from   copper   ores   and   slags,    may   be   best 
standardized    by    perfectly    dry,    pure    sodium    oxalate.     The 
strength  of  permanganate  employed  in   " western  methods"  is 
5.643   grams    per  liter.     1    c.c.   is  nearly    equal    to    .005    gram 
calcium  oxide,  CaO.     56.07  parts  of  calcium  oxide,  CaO,  require 
134  parts  of  very  pure  standard  oxalate.     The  salt  should  be 
thoroughly  dried  in  an  air  oven  at   100°  C.  and  preserved  in  a 
small  glass-stoppered  bottle.     Sodium    oxalate   X  .41843   equals 
CaO,  and   1   part  of  iron   (Fe)   equals   .50206  part   of   calcium 
oxide  (CaO). 

41.  Potassium  Permanganate,  for  the  estimation  of  manganese 
by  the  "bismuthate  method/'  is  made  up  very  dilute  and  run 
against  a  special  ferrous-ammonium-sulphate  solution  (42)  or  with 
sodium  arsenite  (47).     A  .03  normal  solution  (1  gram  per  liter) 
will  titrate  convienently  .02  gram  of  manganese  (Mn).     For  rich 
ores,  use  a  .1  normal  solution  (or  3.1  grams  per  liter). 

42.  Special  Ferrous  Ammonium  Sulphate,  for  the  "  bismuth- 
ate  method,"  is  dissolved  to  form  a  solution  of  12.4  grams  of  the 
salt. 

The  concentrated  liquid  is  then  treated  with  50  c.c.  of  a 
mixture  of  equal  volumes  of  strong  sulphuric  acid  and  strong 
phosphoric  acid,  and  diluted  to  exactly  1  liter.  This  will  give 
a  standard  solution  almost  equal  to  the  weaker  .03  normal 
permanganate  (41).  For  .1  normal  permanganate,  use  39.2 
grams  of  the  iron  salt  and  double  the  amount  of  the  two  acids  em- 
ployed. See  volumetric  method  for  chromium  (15,  Chapter  VI). 

43.  Potassium  Thiocyanate,  KSCN,  is  dissolved  and  diluted 
to  such  a  degree  that  1  c.c.  will  precipitate  about  .12  gram  of 


48  ANALYSIS  OF  COPPER 

copper.  Refer  to  solutions  7  and  8,  and  method  1,  Chapter  XII. 
For  ores,  a  more  dilute  solution  of  40  grams  of  the  crystals  per 
liter  is  sufficient,  as  described  in  method  3,  Chapter  IV. 

44.  Silver  Nitrate,  AgNO3,  is  employed  in  method  5,  Chapter 
V,  as  a  precipitant  of  arsenic  acid.     Make  a  10  per  cent  solution 
by  weight  and  use  7  c.c.  for  .1  gram  of  arsenic. 

45.  Silver  Nitrate,  in  method  1,  Chapter  VII,  is  used  as  an 
indicator  in  the  titration  of  nickel.     One  gram  is  dissolved  in 
water,  and  the  solution  brought  to  a  volume  of  1  liter. 

46.  Silver  Nitrate,  for  the  precipitation  of  chlorine  in  copper 
electrolyte,  is  made  up  as  a  normal   solution  of   169.89   grams 
per  liter.      1    c.c.  will  combine  with   .03546  gram   of   chlorine. 
For  very  exact  standardization,  the  solution  would,  of  course, 
be  run  against  standard  salt  solution,  or  standardized  ammonium 
thiocyanate  (No.  9). 

47.  Sodium  Arsenite.  —  A  stock  solution  is  made  by  heating 
in  a  flask  on  a  water  bath  15  grams  of  arsenious  oxide  (As2O3), 
45  g.  of  sodium  carbonate   and   150  c.c.  of   water.     Cool   and 
make  up  to  1000  c.c.  with  water.     A  standard  solution  of  the 
proper  strength  for  titration  of  chromium  or  manganese  in  ores 
or  metals  is  made  by  diluting  300  c.c.  to  1  liter  and  standard- 
izing it   with  permanganate.     The  value  of  the  permanganate 
itself  is  best  obtained  by  comparison  with  pure  sodium  oxalate 
(see  25,  chapter  VI). 

47  a.   Sodium  Citrate,  —  200  grams  per  liter,  is  a  reagent  for 
1,  Chapter  VII. 

48.  Sodium  Chloride,  NaCl,  in  the  assay  of  copper  bullion, 
Chapter  X,  is  a  precipitant  of  silver.     If  19  grams  are  dissolved 
in  1  liter,  1  c.c.  will  precipitate  350  milligrams  of  silver.     Refer 
also  to  No.  17. 

49.  Sodium  Hydroxide,   NaOH,   is    made   up  as  a  normal 
solution  for  the  determination  of  the  free  acid  in  copper  elec- 
trolyte, as  described  in  Chapter  IX.     Dissolve  40  grams  of  the 
purified  sticks  in  1  liter,  and  standardize  against  normal  sul- 
phuric acid,   using  a  .1   per  cent    aqueous  solution  of  methyl 
orange  as   an  indicator.      The  acid   is   valued   by  titrating   it 
against  .8-gram  portions  of  chemically  pure  sodium  carbonate, 
which  has  been  ignited  just  below  a  red  heat. 

50.  Sodium   Thiosulphate   (or  hyposulphite),  Na2S2O3.5H2O, 
is  the  titrating  solution  in  the  " iodide  method"  for  copper  in 


REAGENTS  AND  STANDARD  SOLUTIONS  49 

ores  or  mattes,  as  given  in  method  2,  Chapter  IV,  also  in  method 
22,  Chapter  VI.  If  19.59  grams  are  dissolved  in  1  liter,  1  c.c. 
will  react  with  about  .005  gra*m  of  copper. 

51.  Sodium  Phosphate,  secondary,  Na2HPO4.12H2O,  is  dis- 
solved to  form  a  10  per  cent  solution  of  the  crystals,  for  the 
precipitation  of  either  aluminum,  magnesium,  manganese,  or  zinc. 
The    ammonium    salt   (5),    when    it    is    permissible,    is    prefer- 
able to  the  sodium  compound,  as  the  ammonium  salt  is  easily 
volatilized,  if  traces  are  inclosed  in  a  washed  precipitate. 

52.  Sodium  Sulphide,  Na2S,  as  a  filtered  solution  of  the  pure 
commercial   salt,    extracts    or    separates   the    sulphides   of    the 
" arsenic  group"  of  metals  from  copper,  lead,  or  silver,  but  not  so 
well  from  bismuth,  unless  a  little  potassium  hydroxide  is  added. 

A  filtered  solution  with  a  density  of  1.08  is  diluted  with 
about  two  parts  of  water  for  use  in  copper  analysis.  For  elec- 
trolysis of  antimony  sulphide,  it  is  necessary  to  provide  a  strictly 
colorless  monosulphide.  The  yellow  color  may  be  removed  by 
heating  with  sodium  peroxide,  hydrogen  peroxide,  etc.,  or  the 
sodium  sulphide  may  be  prepared  by  a  method  described  by 
A.  Classen  and  H.  Koch.  Dissolve  about  60  grams  of  the  purest 
commercial  sodium  hydroxide  in  water,  dilute  until  the  liquid 
has  a  density  of  about  1.2,  then  saturate  one  half  of  the  liquid 
with  hydrogen  sulphide.  Add  the  other  half  of  the  solution, 
and  if  the  monosulphide  is  required,  filter  the  solution  directly 
into  stoppered  bottles.  Dilute  for  use,  according  to  conditions. 

53.  Stannous    Chloride,  SnCl2.2H2O,  for  reduction  of  iron. 
Dissolve  metallic  tin  foil  in  hydrochloric  acid,  or  use  the  formula 
of  J.  M.  Camp:  —  Dissolve  300  grams   of  chloride  crystals  in 
500  c.c.  of  strong  hydrochloric  acid  and  500  c.c.  of  water.     Boil 
with  a  few  scraps  of  tin  until   clear  and  then   bottle.     1    c.c. 
reduces  about  1  gram  of  iron. 

54.  Normal  Sulphuric  Acid,  H2SC>4,  is  produced  by  mixing 
with  water  an  amount  of  the  acid  equivalent  to  49.04  grams  of 
the  100  per  cent  acid,  and  then  diluting  to  1  liter.     It  is  stand- 
ardized against  sodium  carbonate  ignited,  and  may  be  compared 
with  normal  sodium,  or  potassium  hydroxides  (Nos.  35  and  49). 
Use  an  aqueous  solution  of  methyl  orange  as  an  indicator,  except 
in  cases  where  bicarbonates  are  to  be  estimated. 

In  very  accurate  work,  the  temperature  should  be  noted 
with  each  titration,  to  apply  a  correction,  if  necessary. 


50  ANALYSIS  OF  COPPER 

55.  Standard  Titanium  Solution,  for  method  13,  Chapter  VII, 
is  prepared  by  dissolving  the  pure  oxide  by  fusing  it,   or  by 
treating  with  10  c.c.  of  hot  strong  sulphuric  acid  and  5  grams 
of  potassium   bisulphate.     The   solution    is    mixed    with   dilute 
sulphuric    acid    at    first,    to    prevent    precipitation.     Then    add 
water  until  1  c.c.  contains  1  milligram  of  titanic  oxide,  Ti02. 

56.  Starch  Indicator  (for  titrations  with  iodine) .  —  According 
to   the  formula  of  J.  M.  Camp,  add  to  .5  gallon   (2  liters)   of 
boiling  water  about  25  grams  of  pure  wheat  starch,  previously 
stirred  up  into  a  thin  paste  with  cold  water.     This  is  boiled  for 
ten  minutes,  and,  when  cold,  about  25  grams  of  pure  zinc  chloride 
dissolved  in  water  are  added  and  the  solution  diluted  to  1  gallon, 
or  3800   c.c.     Mix  thoroughly  and   allow  to  settle  over  night; 
siphon  the  clear  solution  into  a  glass-stoppered  bottle.     It  will 
keep  indefinitely.     This  preparation  is  suitable  for  the  titration 
of  the  acidified  solution  of  cadmium  sulphide  obtained  in  the 
evolution  method  for  sulphur  in  steel. 

57.  Special  Starch  is  prepared  by  hydrolyzing  the  ground 
material   with    1    per   cent    hydrochloric    acid,    allowing    it   to 
stand  over  night  in  the  cold;     then  filtering,  and  washing  with 
cold  water. 

Dry  the  washed  starch  and  heat  for  three  hours  in  the  air 
oven  at  100°  C.  Dissolve  2  grams  of  this  starch  in  500  c.c.  of 
boiling  water,  and  add  15  drops  of  oil  of  cassia  to  prevent 
fermentation  (method  6,  Chapter  XII). 

58.  Zinc  Chloride,  ZnCl2,  finds  its  principal  use  in  a  copper 
laboratory  as  one  ingredient  of  a  concentrated  distilling  solution 
used  by  chemists  in  the  western  states  for  the  distillation   of 
arsenious  chloride  from  the  sulphide  in  the  analysis  of  ores. 

Distilling  Solution.  —  Dissolve  one  pound  (453.6  grams)  of 
chemically  pure  zinc  by  adding  to  it  gradually  a  mixture  of 
1250  c.c.  of  hydrochloric  acid  (d.,  1.2)  and  500  c.c.  of  water. 
When  the  zinc  has  dissolved,  evaporate  the  solution  to  1100  c.c. 
and  mix  the  whole  amount  with  1  liter  of  the  concentrated 
solution  of  cupric  chloride  (No.  17). 


„ 

CHAPTER  IV 

THE  ASSAY  OF  COPPER  IN  ORES  AND  FURNACE  PRODUCTS 

THIS  chapter  is  restricted  to  the  assay  of  copper  in  its  solu- 
tions. The  following  methods  are  in  regular  use  for  the  estima- 
tion of  copper  in  ores,  native  copper,  furnace  by-products,  or 
mill  tailings:  —  (1)  titration  with  potassium  iodide; 1  (2)  tit  ration 
with  potassium  cyanide;2  (3)  precipitation  with  potassium  thio- 
cyanate  and  titration  of  the  resulting  compound  with  potassium 
permanganate  in  presence  of  excess  of  caustic  alkali;3  (4)  the 
colorimetric  assay;4  (5-9)  electro-analysis.5 

The  selection  of  method  varies  with  the  character  of  the 
material  and  the  preference  of  the  chemist,  but  the  electrolytic 
assay  is  the  most  accurate. 

1.  Titration  by  Iodide.1  —  According  to  standard  western 
practice,  the  weighed  sample  of  1  gram  (.5  for  ores  over  25 
per  cent  copper),  is  decomposed  in  a  3-inch  (7.5  cm.)  casserole 
by  treatment  with  nitric  and  hydrochloric  acid  in  excess  and 
10  c.c.  of  sulphuric  acid. 

Evaporate  until  dense  white  fumes  of  the  last  acid  are 
evolved.  After  cooling,  dilute  with  water  and  boil  until  all 
soluble  sulphates  are  in  solution.  Filter  off  the  insoluble  residue 
and  wash  well  with  hot  water,  allowing  the  filtrate  and  washings 
to  run  into  a  350  c.c.  beaker.  To  this  filtrate  add  10  c.c.  of  a 
saturated  solution  of  sodium  thiosulphate  and  boil  until  the 
precipitated  sulphides  settle  readily.  Filter  and  wash  with  cold 
water  until  free  from  iron  salts  (usually  4  to  7  times).  Carefully 
wrap  the  paper,  fold  it  into  a  dry  filter,  and  place  it  in  a  porce- 
lain crucible.  The  crucibles  are  placed  in  a  muffle  that  is  kept 

1  Method  1.     Eng.  and  Min.  Jour.  89,  498;   /.  Am.  Chem.  Soc.  24  (1902), 
1082  and  580;   Eng.  and  Min.  Jour.  Nov.  17,  1904;  (1910)  1221;  74  (1902), 
846. 

2  Low's  Technical  Analysis.     3  J.  Am.  Chem.  Soc.  20  (1898),  610. 

4  J.  Am.  Chem.  Soc.  19  (1897),  24;   Trans.  A.  I.  M.  E.  30,  851. 

5  Eng.  and  Min.  Jour.  84,  773;  also  77  (1909),  159;  94,  315.     J.  Am. 
Chem.  Soc.  Nov.  1907.     El.  Chem.  and  Met.  Ind.  6,  19  and  58. 


52  ANALYSIS  OF  COPPER 

barely  red  hot,  to  roast  and  dry  the  precipitate,  thus  removing 
the  sulphur  and  much  of  the  arsenic.  Too  much  heat  must  be 
carefully  avoided  at  this  stage,  or  the  mass  will  spit  before  it  is 
dry,  and  later  on  will  fuse  into  the  porcelain.  It  is  to  prevent 
" spitting"  that  the  extra  filter  paper  is  used,  and  when  properly 
ignited,  the  residue  will  be  found  enveloped  in  ash,  and .  easily 
transferable  to  a  flask. 

Now  transfer  the  residue  to  a  small  "  copper  flask,"  decompose 
it  with  5  c.c.  of  nitric  acid-potassium  chlorate  mixture,  and 
evaporate  almost  to  dryness  to  oxidize  any  remaining  arsenic,  etc. 
Add  dilute  ammonia  to  alkaline  reaction  and  boil  the  liquid  well 
for  two  minutes.  Acidify  slightly  with  acetic  acid  without  boil- 
ing, cool,  and  add  about  3  grams  of  solid  potassium  iodide. 
Determine  the  copper  by  titration  with  sodium  thiosulphate 
(Na2S2O3),  using  starch  as  an  indicator.  (Solutions  48  and  54, 
Chapter  III.) 

The  Western  chemists,  just  quoted,  did  not  find  the 
reduction  of  copper  by  aluminum  to  be  satisfactory.  It  not 
only  took  more  time,  but  with  special  ores  and  conditions,  the 
precipitation  was  not  complete.  Besides,  particles  of  the  fine 
copper  were  easily  lost  on  filtering,  or  were  oxidized  and  dis- 
solved by  the  wash  water. 

Reduction  by  Aluminum.  —  A.  M.  Fairlie,1  A.  H.  Low,2  and 
others  prevent  oxidation  of  the  copper  by  the  addition 
of  15  c.c.  of  hydrogen  sulphide  water  as  soon  as  the  reduc- 
tion by  aluminum  is  completed.  This  scheme  prevents  the 
formation  of  a  bulky  mass  of  sulphides  from  rich  ores.  If  such 
reduction  is  preferred,  it  may  be  effected  after  all  silver  chloride 
has  been  filtered  off,  by  boiling  the  sulphuric  solution  in  a  wide  lip- 
less  beaker  with  three  pieces  of  sheet  aluminum,  each  1^  inches 
(or  3.8  cm.)  square.  Continue  the  boiling  until  the  copper  is 
out  of  solution  and  the  aluminum  appears  bright  and  clean  on 
shaking.  Pour  through  a  9  cm.  filter  directly  after  the  addition 
of  the  hydrogen  sulphide  water,  but  hold  back  most  of  the  metal 
and  wash  it  two  or  three  times  with  diluted  hydrogen  sulphide 
water.  Drain  thoroughly  and  redissolve  through  the  funnel  by 
10  c.c.  of  dilute  (1:1)  nitric  acid.  Finally,  wash  the  aluminum 

1  Eng.  and  Min.  Jour.  84,  773;   also  77  (1909),  159;   94,  315.    J.  Am. 
Chem.  Soc.  Nov.  1907.    El.  Chem.  and  Met.  Ind..  6,  19  and  58. 

2  J.  Am.  Chem.  Soc.  30  (1908),  760. 


•COPPER  IN  ORES  AND  FURNACE  PRODUCTS  53 

well,  cleanse  any  sulphur  on  the  filter  by  treatment  with  5  c.c. 
of  saturated  bromine  water,  and.  finish  the  washing  with  hot 
water.  Boil  out  all  the  bromine1  and  titrate  by  iodine  as  before. 

Kendall 1  recommends,  the  addition  of  sodium  hypochlorite 
and  phenol  in  order  to  secure  more  even  results  in  the  titration, 
and  A.  H.  Low2  advises  a  slight  boiling  after  the  addition  of  the 
acetic  acid  to  prevent  a  return  of  color  after  titration.  Refer 
also  to  the  special  " iodide"  titration  of  nickel  in  nickeliferous 
copper  matte  (14,  Chapter  VI). 

2.  Titration  with  Potassium  Cyanide.2  —  The  action  of  this 
reagent  on  copper  solution  is  a  function  of  several  variables. 
The  conditions  observed  in  standardization  must  be  exactly 
observed  in  the  work  on  the  ore  samples.  The  main  points  are 
uniform  temperature,  regularity  in  titration,  the  same  excess  of 
alkali,  and  the  same  final  volume,  in  each  case. 

Standard  Solution.  —  22.5  grams  of  chemically  pure  potassium 
cyanide  per  liter  make  a  solution,  1  c.c.  of  which  will  have  a 
value  of  about  .005  gram  of  copper.  Refer  to  formula  28  of 
Chapter  III. 

Unless  the  ores  are  very  impure,  western  operators  usually 
prefer  to  standardize  against  matte,  or  ores,  in  which  the  copper 
contents  have  been  determined  electrolytically.  Others  prefer, 
instead,  to  take  .2  gram  to  .3  gram  of  chemically  pure  copper 
foil,  dissolve  in  5  c.c.  of  strong  nitric  acid,  dilute  with  5  c.c.  of 
saturated  bromine  water  plus  25  c.c.  of  distilled  water,  and  boil 
out  the  bromine.  Add  10  c.c.  of  ammonia  (d.,  .90)  with  50  c.c. 
of  water  and  cool  quickly  to  room  temperature,  then  titrate 
exactly  as  for  ores. 

The  standard  cyanide  is  subject  to  change,  and  it  is  necessary 
to  protect  the  liquid  from  the  sun,  or  any  strong  light,  and 
retest  it  frequently. 

(a)  Assay  of  Pure  Ores.  —  Such  ores,  or  standard  mattes, 
are  dissolved  in  nitric  acid.  Add  10  c.c.  of  strong  acid  to  1 
gram  of  sample  in  a  500  c.c.  flask.  Take  only  .5  gram  when 
over  25  per  cent  copper.  Heat  on  a  steam  bath  until  the  brown 
fumes  are  driven  off,  then  add  200  c.c.  of  cold  water  and  20  c.c. 
of  ammonium  hydroxide  (d.,  .90).  Titrate  slowly,  adding  po- 
tassium cyanide  in  small  amounts  only  and  allowing  the  deposit 

1  J.  Am.  Chem.  Soc.,  33  (1911),  1947;  34,  347. 

2  Personal  communications. 


54  ANALYSIS  OF  COPPER 

to  settle  after  each  addition.  When  the  solution  in  the  flask 
is  a  pale  violet  color,  filter  into  another  500  c.c.  flask  and  add 
the  cyanide  until  colorless.  The  burette  reading  is  multiplied 
by  the  factor  for  its  copper  value,  which  is  determined  by  run- 
ning a  half-gram  sample  of  "standard"  matte  as  a  standard 
with  each  set  of  assays. 

(6)  Samples  containing  organic  matter,  or  much  arsenic  or 
manganese,  are  decomposed  with  nitric  acid  and  a  small  amount 
of  potassium  chlorate.  Large  amounts  of  organic  matter  may 
keep  some  iron  in  solution,  producing  greenish  tints.  In  this 
case,  roast  sample  gently  in  a  scorifier;  then  treat  the  residue 
in  a  platinum  dish  with  5  c.c.  of  nitric  acid,  5  c.c.  hydrofluoric 
acid,  and  2  c.c.  sulphuric  acid,  and  evaporate  to  fumes  of  sul- 
phuric anhydride.  Add  5  to  10  c.c.  of  nitric  acid,  wash  into  the 
flask,  and  proceed  as  before.  Good  results  are  often  obtained 
by  adding  small  portions  of  potassium  chlorate  to  the  boiling 
nitric  acid  solution.  Some  oxidized  ores  and  slags  require  a 
preliminary  treatment  with  hydrochloric  acid  or  the  addition 
of  hydrofluoric  acid  for  complete  solution  of  the  copper.  In 
such  a  case,  add  5  c.c.  of  each  of  the  acids,  heat  gently  for  ten 
minutes,  add  10  c.c.  of  nitric  acid,  and  take  to  dryness.  Take 
up  with  water  and  5  to  10  c.c.  of  nitric  acid,  wash  into  the  flask, 
and  proceed  as  before.  If  much  silver  is  present,  remove  it  with 
a  few  'drops  of  hydrochloric  acid  before  adding  the  ammonia  to 
any  of  the  samples  under  treatment. 

(c)  Impure  Ores,  or  Mattes,  etc.  —  In  presence  of  much  zinc, 
cobalt,  or  nickel,  a  preliminary  separation  of  the  copper  must  be 
made,  preferably  by  sodium  thiosulphate,  as  in  method  1.  The 
roasted  sulphides  should  be  dissolved  in  nitric  acid  and  titrated 
as  before,  except  that  chemically  pure  copper  foil  is  used  for  the 
standard,  because  the  titration  is  made  in  the  absence  of  iron. 

3.  Thiocyanate  Method  (By  F.  G.  Hawley).1  —  Weigh  .5 
to  1  gram  of  ore  into  a  tall  300  c.c.  beaker,  add  12.5  c.c.  of  "acid 
mixture"  (1  part  sulphuric  acid,  2  parts  nitric  acid  and  1  of  a  satu- 
rated solution  of  potassium  chlorate  in  nitric  acid).  Then,  when 
nearly  decomposed,  add  10  drops  of  hydrofluoric  acid,  evaporate 
to  strong  white  fumes  of  sulphuric  acid,  and  cool  the  residue. 
Add  60  c.c.  of  water  and  just  neutralize  with  ammonia.  Add 
5  c.c.  of  hydrochloric  acid,  then  10  to  12  c.c.  (according  to  cop- 
1  Eng.  and  Min.  Jour.  90  (1910),  647. 


COPPER  IN  ORES  AND   FURNACE  PRODUCTS  55 

per  content)  of  potassium  thiocyanate  (40  grams  per  liter). 
Boil  for  two  minutes  and  remove ^from  the  plate.  Let  the  beaker 
stand  for  5  minutes  covered,  then  for  5  minutes  uncovered,  and 
filter  through  a  12.5  cm.  jilter,  No*  597  S.  and  S.  Wash  four  times 
with  hot  water  (60  to  70°),  then  place  the  original  beaker  under  the 
funnel,  and,  with  a  wash  bottle,  treat  the  copper  salt  with  a 
boiling  5  per  cent  solution  of  sodium  hydroxide.  Use  a  medium 
fine  jet  and  stir  the  precipitate  thoroughly.-  Wash  four  times 
with  hot  water,  cool  the  filtrate  somewhat,  make  acid  with 
slightly  diluted  sulphuric  acid,  and  immediately  titrate  with 
standard  potassium  permanganate,  —  of  which  1  c.c.  equals  .01 
gram  of  metallic  iron,  Fe.  High  coppers  should  be  titrated  cold 
and  in  a  volume  of  not  less  than  200  c.c.  A  conversion  table 
is  employed.  The  thiocyanate  may  also  be  dissolved  as  in  5c 
and  the  solution  electrolyzed. 

3a.  Method  of  D.  J.  Demorest.1  —  This  modification  is  said 
to  permit  an  accurate  titration  by  permanganate  without  the  use 
of  any  empirical  conversion  table.  Weigh  out  enough  of  the  ore 
to  have  present  .05  to  .30  gram  of  copper.  Transfer  the  sam- 
ple to  a  200  c.c.  beaker,  add  5  c.c.  of  strong  hydrochloric  acid, 
and  heat  for  several  minutes;  then  add  10  c.c.  of  nitric  acid  and 
digest  on  a  hot  plate  until  the 'ore  is  completely  decomposed. 
Then  add  10  c.c.  of  (1:1)  sulphuric  acid  and  boil  down  until 
white  fumes  appear.  Cool,  add  50  c.c.  of  water  containing 
3  grams  of  tartaric  acid,  and  heat  until  all  soluble  salts  are 
in  solution. 

Cool  and  add  ammonia  until  the  solution  turns  a  deep  blue, 
then  add  sulphuric  acid  until  the  liquid  is  just  acid,  then  1  c.c. 
more.  Now  add  1  gram  of  sodium  sulphite  dissolved  in  20  c.c. 
of  water,  heat  nearly  to  boiling,  and  add  slowly,  with  vigorous 
stirring,  one  gram  of  potassium  thiocyanate  dissolved  in  20  c.c. 
of  water.  Heat  at  a  nearly  boiling  temperature  for  several 
minutes  to  coagulate  the  precipitate  and  dissolve  out  all  the 
tartaric  acid.  Cool  somewhat  and  filter  hot,  preferably  through 
an  asbestos  mat  on  a  Gooch  filter.  Wash  well  with  water  and 
rinse  out  the  suction  flask.  Then  pour  through  the  felt  30  c.c. 
of  a  hot  10  per  cent  sodium  hydroxide  solution  and  wash  well 
with  water.  The  assay  should  be  finished  hot. 

Warm  the  filtrate  to  about  50°  and  titrate,  running  in  the 
1  J.  Ind.  and  Eng.  Chem.  5  (1913),  215. 


56  ANALYSIS  OF  COPPER 

permanganate  slowly  and  shaking  the  flask  vigorously.  The 
solution  turns  green.  After  about  10  c.c.  have  been  run  in, 
take  out  a  drop  of  liquid,  place  it  in  a  drop  of  hydrochloric  acid 
on  a  white  paraffined  plate,  and  add  a  drop  of  10  per  cent  ferric 
chloride  solution.  If  a  red  color  appears,  continue  to  add  the 
permanganate,  testing  after  each  5  c.c.  until  the  red  becomes 
weaker,  then  test  often  until  the  red  tint  is  faint.  Add  30  c.c. 
of  (1:1)  sulphuric  *  acid,  shake  until  dissolved,  and  finish  the 
titration.  The  copper  value  is  .1897  times  the  iron  value. 
Refer  to  methods  5c  and  8  for  electrolytic  modifications  of 
the  thiocyanate  method.  For  safety,  titrate  under  a  hood. 

4a.  The  Colorimetric  Assay.  Western  Method  (after  Thorn 
Smith) .  —  Standards  for  the  assay  of  blast  furnace  slags  are 
prepared  as  follows:  Take  3  grams  of  sample  of  an  ore, 
tested  electrolytically,  cover  it  with  water,  add  10  c.c.  of 
nitric  acid  (d.,  1.  4)  and  1  c.c.  of  hydrochloric  (d.,  1.  2); 
heat  for  a  few  minutes  on  a  steam  bath;  dilute  with  100 
c.c.  of  water,  and  then  add  a  slight  excess  of  dilute 
ammonia.  Filter  into  bottles  of  uniform  size,  for  compari- 
son of  color,  and  wash  until  the  bottle  is  filled  to  the  200 
c.c.  mark.  If  the  true  copper  in  this  sample  was  .20  per 
cent,  this  standard  is  called  'B.  2.  To  prepare  B.  3,  add 
.003  gram  of  copper  to  another  3  grams  of  the  same  sample. 
B.  4  is  prepared  by  adding  .006  gram  copper  and  B.  5  by  add- 
ing .009  gram  of  copper,  the  copper  always  being  added  before 
the  ammonia  and  the  samples  each  treated  as  with  B.  2. 

Tailings.  —  Heat  1  gram  of  sample  on  the  steam  bath  with 
5  c.c.  of  nitric  acid  and  a  pinch  of  potassium  chlorate;  dilute, 
filter,  and  wash  as  in  the  assay  of  slags.  If  the  copper  per  cent 
by  electrolysis  was  .50,  this  standard  is  called  T.  5.  To  pre- 
pare T.  6,  add  .001  gram  of  copper  to  anothe^  1-gram  sample; 
.002  gram  for  T.  7;  .003  gram  for  T.8;  .004  gram  for  T.  9; 
.005  gram  for  T.  10. 

Reverberatory  Slags.  —  Take  2  grams  of  any  of  the  Mon- 
tana, or  Arizona,  products,  add  10  c.c.  of  hydrochloric  acid  and 
2  c.c.  of  nitric  acid.  Heat,  dilute,  filter  after  the  addition  of 
ammonia,  and  wash  as  in  tests  of  slags  from  cupolas.  If  the 
true  copper  on  this  sample  was  .30  per  cent,  this  standard  is 
called  R.  3.  To  prepare  R.  4,  add  .002  gram  of  copper  to 
another  2  grams  of  sample.  Add  .004  grams  for  R.  5,  and 


COPPER  IN  ORES  AND  FURNACE  PRODUCTS 


57 


treat  each  as  in  the  preparation  of  R.  3.  If  samples  low  enough 
to  furnish  the  lowest  standard  -are  not  at  hand,  remove  the 
copper  first  by  electrolysis  from  a  sample  and  then  add  the  re- 
quired amount  of  pure^standarcl  copper  solution  for  the  first 
number  in  the  set. 

A  set  of  standards  having  been  prepared  for  each  product 
as  above,  another  set  of  bottles  is  filled  almost  to  the  mark  with 
water  and  10  c.c.  of  ammonium  hydroxide  (.90).  A  standard 
solution,  containing  .001  gram  of  copper  to  the  c.c.,  is  then  run 
into  each  from  a  burette  until  the  color  matches  the  above 
standards,  and  the  burette  reading  in  each  case  is  carefully  noted. 
The  following  results  were  obtained  by  the  chemists.  From  this 
table  prepare  the  standards. 

BURETTE  READINGS  FOR  STANDARDS 


B.2  required  4.4  cc. 
B.3        "         6.7  " 

R.2  required 
R.3 

3.2  cc. 
4.6   " 

T.4  required 
T.5 

3.8  cc. 

4.7    " 

B.4        "         9.1  " 

R.4 

6.1   " 

T.6 

5.7    " 

B.5        "       11.1  " 

R.5 

7.9   " 

T.7 

6.6    " 

R.6 

9.7  " 

T.8 

7.6    " 

R.7 

11.4  " 

T.9 

8.5    " 

R.8 

13.2  " 

T.10      " 

9.5    " 

Determination  of  Copper  (in  unknown  samples) .  —  Treat  the 
blast,  reverberatory  slags,  or  tailings,  exactly  as  described 
above  and  match  the  filtrates  with  the  standards,  which  were 
prepared  by  separating  the  copper  in  presence  of  nearly  the 
same  interfering  elements  found  in  the  regular  works  samples 
reported  to  the  office  for  analysis. 

4b.  Lake  Superior  Method.  —  The  color  test  has  been  super- 
seded by  rapid  electrolysis  in  testing  slags  or  tailings  high  in 
soluble  iron,  but  is  still  found  useful  for  the  classification  of  lots 
of  sludges  from  the  diamond  drill,  and  for  the  rapid  assay  of 
Lake  mill  tailings,  and  assay  slags  from  the  fire  assays  of  native 
copper  products.  The  permanent  standards  are  diluted  from  a 
strong  solution  to  the  uniform  volume  of  200  c.c.  by  means  of 
dilute  ammonia,  1  volume  of  ammonia  (d.,  .9)  to  6  volumes  of 
water.  If  preserved  in  thin-walled,  cylindrical  bottles  with  tight 
glass  stoppers,  the  solutions  will  remain  unchanged  for  about  a 
year.  Oil  sample  bottles  will  answer  but  are  inferior. 

2.5  grams  of  sample  are  taken  as  a  standard  sample  for 
analysis  and  also  for  the  set  of  standards.  Dissolve  .3  gram 


58  ANALYSIS  OF  COPPER 

of  pure  copper  in  5  c.c.  of  nitric  acid  in  a  500  c.c.  flask,  treat 
with  5  c.c.  of  sulphuric  acid,  boil  out  the  nitric  acid,  and  make 
the  solution  up  to  1500  c.c.  with  dilute  ammonia  as  already 
described.  Then  1  c.c. '  contains  .0002  gram  of  copper. 

Fill  a  burette  with  the  well-mixed  solution  and  run  into  each 
standard  bottle  the  amount  required  to  make  a  set  ranging  from 
.1  to  1  per  cent  of  2.5  grams. 

The  diameter  of  the  bottles  is  4.4  cm.  and  the  height  to  the 
200  c.c.  mark,  15.2  cm. 

Cupola  Slags.  —  Treat  2.5  grams  of  powdered  slag  in  a  No.  4 
porcelain  casserole  with  7  c.c.  of  nitric,  7  c.c.  of  sulphuric  acid, 
and  7  c.c.  of  water.  Warm,  and  finally  boil  down  to  white  fumes 
over  a  Bunsen  burner,  stirring  to  break  up  any  clots  and  form 
a  paste. 

Stir  in  50  c.c.  of  water  while  still  warm  and,  when  the  soluble 
salts  are  dissolved,  add  sufficient  ammonium  hydroxide  to  pre- 
cipitate the  iron  and  alumina.  Pour  the  solution  through  a  No.  3 
Munktell  15  cm.  filter  into  a  bottle  of  the  same  volume  as  the 
standard  set. 

Wash  the  mass  with  dilute  ammonia  until  the  washings 
appear  colorless,  and  then  make  the  solution  up  to  the  200  c.c. 
mark  with  the  same  dilute  ammonia  prescribed  for  the  standards. 
When  the  bottle  is  nearly  filled,  if  the  tint  on  shaking  appears 
greener  than  the  standard  bottle  of  about  the  same  depth  of 
color,  then  complete  the  dilution  with  pure  water  instead  of 
ammonia.  If  the  ferrous  oxide  is  over  10  per  cent,  the  first 
precipitate  of  ferric  hydroxide  should  be  washed  only  once, 
drained,  and  then  washed  back  into  the  casserole  with  a  jet  of 
water,  using  as  little  as  possible.  Redissolve  the  iron  in  a  very 
little  dilute  sulphuric  acid,  precipitate  again  with  a  little  ammonia, 
run  through  the  filter  into  the  bottle,  and  wash  until  the  filtrate 
is  clear. 

4c.  Color  Test  of  Mansfeld  Shales.  —  H.  Koch  weighs  2 
grams  of  substance  into  a  small  porcelain  crucible  and  roasts  the 
contents  on  a  sand  bath,  afterwards  decomposing  the  sample 
exactly  as  in  the  electrolytic  assay  of  ore  and  shales  (method  5). 
From  the  residue  on  evaporation,  the  sulphate  of  copper  is  dis- 
solved as  usual,  then  the  solution  (50  c.c.)  with  the  residue  is 
transferred  to  a  thick-walled,  cylindrical  glass,  6  to  7  cm.  wide 
and  14  cm.  high,  which  is  marked  at  250  cm.  After  the  addi- 


COPPER  IN  ORES  AND  FURNACE  PRODUCTS  59 

tion  of  30  c.c.  ammonium  hydroxide  (d.,  .91),  it  is  filled  to  the 
mark  with  water  and  stirred.  After  settling,  the  fluid  is  passed 
through  a  dry  14  cm.  filter  intb  a  square-cornered  bottle  with 
ground  sides.  The  area.«of  the  battle  adopted  is  60  by  40  mm., 
the  height  to  shoulder  about  70  mm.,  and  the  whole  contents 
about  110  cm.;  the  thickness  of  the  walls  must  be  uniform. 

The  copper  values  are  ascertained  by  comparison  with 
standard  solutions  which  are  prepared  in  the  central  labora- 
tory from  shales  of  known  copper  content.  The  copper  is 
usually  calculated  in  kilos  per  metric  ton.  The  minus  error 
increases  with  the  copper,  just  as  in  tests  on  American  ores  or 
slags,  hence  the  standard  solutions  are  prepared  according  to  an 
empirical  scale  of  perhaps  20  bottles,  to  read  colors  from  ma- 
terial varying  in  copper  contents  from  2  kg.  to  140  kg.  per  ton. 

The  copper  in  shales  of  the  usual  contents  of  25  to  35  kg. 
(2.5  to  3.5  per  cent)  is  estimated  with  an  accuracy  of  1  kg.  per 
metric  ton  (.1  per  cent). 

5.  Copper  by  Electrolysis.  —  In  routine  work,  as  observed  by 
A.  M.  Smoot,  the  electrolytic  assay  has  advantages  over  all 
others,  because  it  is  applicable  to  any  sample  from  refined  copper 
to  the  lowest  tailings;  and  further,  it  admits  the  use  of.  large 
charges,  thus  dividing  the  errors  inherent  in  all  such  processes, 
which  is  an  especial  advantage  with  high  grade  material.  This 
fact  is  so  well  recognized  that  practically  no  other  method  is 
used  by  large  firms  for  control  and  umpire  assays. 

It  is  wrong  to  assume,  however,  that  the  copper  is  thus  per- 
fectly separated  from  other  associated  elements,  and  even  with 
the  purest  refined  copper,  high  results  may  be  obtained  by  oxida- 
tion of  the  cathode  or  by  occlusion  of  gases  by  the  deposit.  A 
preliminary  separation  of  copper  from  associated  impurities  is 
sometimes  necessary,  thus  making  the  electrolysis  a  finishing 
process  to  obtain  a  weighable  deposit. 

Chemists  are  referred  to  Chapter  I  for  a  description  of  the 
most  convenient  apparatus.  Perforated  cathodes  are  described 
in  1,  Chapter  XI. 

Acid  Electrolyte.  —  In  Western  reduction  works,  nitric  acid  is 
often  used  alone,  particularly  with  leady  gres,  if  a  deposit  of  lead 
peroxide  is  also  required,  but  there  is  a  tendency  to  oxidation 
of  copper  unless  the  per  cent  of  copper  is  small  and  the  time  of 
deposition  rather  short.  In  accurate  work  on  metallic  copper 


60  ANALYSIS  OF  COPPER 

(Chapter  XI),  sulphuric  acid  is  therefore  added  in  such  amount 
that  when  the  electrolysis  is  completed,  sufficient  free  sulphuric 
acid  shall  be  present  to  retain  arsenic,  iron,  and  other  impurities 
in  solution  after  the  greater  part  of  the  nitric  acid  has  been  re- 
duced to  ammonia  by  the  electric  current. 

5a.  Western  Assay  of  Sulphide  Ores.  —  Weigh  1  gram 
of  ore  into  a  beaker  (3.5  inches  high  and  2.25  inches  diameter); 
add  8  c.c.  of  nitric  acid  and  a  little  potassium  chlorate.  Take 
to  complete  dryness  on  the  steam  bath.  Take  up  with  water 
and  6  to  10  c.c.  of  nitric  acid,  fill  the  beaker  with  water, 
allow  to  settle,  and  place  on  the  battery.  It  is  often  better  to 
use  a  little  sulphuric  acid,  2  to  5  c.c.,  and  drive  off  nearly  all 
the  nitric  acid,  finally  adding  an  exact  amount  (4  c.c.)  of  nitric 
before  electrolysis. 

5b.  Oxidized  Ores.  —  Take  a  one-gram  sample  to  dryness 
with  8  c.c.  of  nitric  acid;  add  10  c,c.  of  hydrochloric  acid  and 
2  c.c.  of  sulphuric  acid  and  take  down  to  fumes  of  sulphuric 
anhydride.  Dissolve  the  salts  with  8  c.c.  of  nitric  acid  and 
water,  allow  to  settle,  and  place  on  the  battery. 

5c.  Mattes.  —  Moisten  a  one-gram  sample  with  a  few  drops 
of  water,  add  8  c.c.  of  nitric  acid  and  1  c.c.  of  sulphuric  acid, 
and  take  to  dryness  on  a  steam  bath.  Dissolve  with  water  and 
8  c.c.  of  nitric  acid,  filter,  and  electrolyze.  The  percentage  of 
silver,  as  determined  by  fire  assay,  is  deducted  from  the  per- 
centage of  copper  plus  silver  found  by  electrolysis.  291.66  ounces 
per  ton  equals  1  per  cent.  If  the  silver  is  considerable,  it  may 
be  precipitated  with  just  sufficient  dilute  hydrochloric  acid, 
avoiding  an  excess.  The  silver  chloride  is  filtered  off,  the  traces 
of  hydrochloric  acid  removed  by  evaporation  and  the  copper 
alone  deposited  by  the  current. 

5d.  Western  Slags.  —  Decompose  2  grams  in  a  platinum 
dish  with  6  c.c.  of  nitric  acid,  8  c.c.  of  hydrofluoric  acid,  1 
to  2  c.c.  of  sulphuric  acid,  and  evaporate  to  white  fumes.  Take 
up  with  water  and  10  c.c.  of  sulphuric  acid  and  place  on  the 
battery.  Allow  about  .11  ampere  per  assay  (with  a  110-volt 
current);  this  gives  a  potential  of  1.4  to  2.3  volts  across  the  elec- 
trode terminals  of  each  assay.  Finally,  test  a  little  of  the  liquid 
with  a  drop  of  hydrogen  sulphide  water  on  a  spot  plate  to  prove 
that  the  copper  has  all  been  deposited.  Wash  the  platinum 
cathodes  first  by  dropping  them  very  rapidly  into  a  beaker  of 


COPPER  IN  ORES  AND  FURNACE  PRODUCTS  61 

water,  then  by  a  jet  from  a  bottle.  Remove  the  water  by  means 
of  94  per  cent  denatured  alcohol,  carefully  burn  off  the  slight 
excess  of  alcohol  (keeping  the  plate  in  rapid  motion)  and  then 
cool  and  weigh  the  cathodes. 

If  the  deposits  are  either  slightly  grayish,  or  show  dark  spots 
due  to  arsenic,  they  may  be  dissolved  in  8  c.c.  of  nitric  acid, 
or  in  an  acid  mixture,  and  the  copper  again  deposited,  removing 
the  electrode  just  as  soon  as  the  process  is  completed.  Copper 
in  ores  and  furnace  products  may  be  separated  from  bismuth, 
antimony,  and  arsenic  by  precipitation  as  thiocyanate  (3).  The 
white  salt  is  washed  thoroughly,  carefully  ignited  in  a  porcelain 
crucible,  dissolved  in  7  c.c.  of  nitric  acid,  and  the  copper  esti- 
mated by  electrolysis  as  before.  Instead  of  igniting  the  precipi- 
tate, the  excess  of  ammonium  thiocyanate  may  be  destroyed  by 
evaporation  with  nitric  acid.  Compare  also  ''Eastern  methods.'7 

6.  Lake  Superior  Method  for  Chilled  Slags.  —  If  a  sample  of 
slag,  or  other  furnace  product,  is  evaporated  to  fumes  with  acids, 
without  any  addition  of  hydrofluoric  acid,  enough  copper  is  fre- 
quently retained  in  the  silica  to  cause  a  serious  error.  One  of 
the  author's  assistants  noted  that  chilled  slags,  granulated  in 
water,  are  almost  completely  soluble  in  dilute  boiling  sulphuric 
acid  without  separation  of  silica.  The  copper  is  thus  taken 
entirely  into  solution.  Grind  the  slag  to  pass  through  a  sieve 
of  100  meshes  to  the  linear  inch  (40  per  cm.). 

Weigh  2  grams  of  the  powder,  from  which  any  shot  has  been 
sifted  out  and  separately  weighed.  Transfer  from  the  balanced 
watch  glass  to  a  tall  300  c.c.  lipless  beaker,  12.5  cm.  (5  inches)  in 
height,  and  5.7  cm.  in  diameter.  Add  80  to  100  c.c  of  distilled 
water,  stirring  rapidly  until  the  sample  is  entirely  in  suspension. 
Continue  the  rapid  stirring  and  add  from  a  graduate  12  c.c.  of 
sulphuric  acid  (d.,  1.84),  place  over  a  lamp,  and  bring  to  boiling, 
while  stirring  to  preserve  the  suspended  condition.  Boil  for 
about  three  minutes,  and  break  up  any  particles  of  slag  which 
may  have  settled.  The  solution  should  be  clear  or  slightly  milky 
and  no  more  than  a  trace  of  silica  should  remain  on  the  bottom. 

Now  add  carefully  three  or  four  drops  of  nitric  acid.  A 
violent  effervescence  will  ensue.  As  this  subsides,  and  the  iron 
rapidly  changes  to  the  ferric  state,  add  7  c.c.  of  nitric  acid  if 
the  copper  is  to  be  deposited  over  night,  or  8  to  9  c.c.  if  the  cop- 
per assay  is  to  be  placed  in  the  Frary  rotary  device,  or  in  con- 


62  ANALYSIS  OF  COPPER 

nection  with  a  rotating  anode  spindle.  Dilute  to  150  c.c.,  and 
electrolyze  over  night  with  a  current  of  .8  to  1  ampere  per  assay, 
or  in  the  rotary  device  with  3  to  4.5  amperes.  When  the  copper 
is  nearly  deposited,  wash  down  the  split  cover  glasses,  and,  a 
few  minutes  later,  test  with  hydrogen  teulphide  water  on  a  porce- 
lain spot  plate  in  the  usual  manner.  In  the  case  of  yellow 
solutions,  the  color  of  the  test  should  be  compared  with  some 
untreated  solution.  Wash  the  plates  rapidly  with  water  and 
alcohol,  ignite,  and  weigh  as  in  the  preceding  method.  In  the 
Frary  solenoid,  the  deposition  of  the  copper  may  be  completed 
in  45  to  90  minutes,  but  the  current  should  not  be  allowed  to 
act  long  after  the  deposition  is  complete.  The  solutions  must 
be  kept  cold,  or  the  copper  may  commence  to  redissolve.  A 
solenoid  may  be  cooled  by  the  circulation  of  cold  water  be- 
tween the  beaker  and  copper  cylinder,  if  it  is  to  be  kept  in  con- 
tinuous operation.  The  operator  should  then  be  able  to  increase 
the  current  to  4.5  amperes  per  square  decimeter,  and  complete 
the  electrolysis  of  a  sample  of  waste  blast  furnace  slag  in  half 
an  hour.  Such  a  method  is  fairly  rapid  and  far  more  accurate 
than  any  color  test. 

The  platinum  cathode  is  made  from  a  sheet  5  cm.  high  and 
10  cm.  wide,  giving  a  total  immersed  depositing  surface  of  100 
sq.  cm.,  or  1  sq.  decimeter,  which  will  be  regarded  as  a  normal 
area  in  the  measurement  of  current  density. 

UMPIRE  AND  CONTROL  ASSAYS  AT  THE  PORT  OF  NEW  YORK 

7.  Siliceous  Ores.1  —  Such  material  is  generally  tested,  when 
high-grade,  by  the  same  method  to  be  prescribed  for  high-grade 
matte.     As  much  as  3  to  5  grams  are  taken  if  the   ore  is   low- 
grade.     A  small  amount  of  copper  may  be  deposited  in  6  to  8 
hours  with  a  current  of  .25  ampere.     The  large  samples  taken 
for  electrolysis  render  these  methods  more  suitable  for  umpire 
work    than    the   more   rapid    titrations    generally   used   in   the 
western  part  of  the  United  States. 

8.  Heavy  Sulphides ;    Thiosulphate  Modification.  —  Pyritous 
ores  usually   contain   impurities  which   would   contaminate   the 
copper  deposits,  and  the  presence  of  much  sulphate  of  iron  in 
the  electrolyte  causes  interference,  just  as  it  does  in  the  assay  of 

1  A.  M.  Smoot,  personal  communication. 


COPPER  IN  ORES  AND  FURNACE  PRODUCTS  63 

ferruginous  reverberatory  or  blast  furnace  slags  from  native 
copper.  In  the  case  of  rich  ores,  the  nitric  acid  should  nearly 
all  be  driven  out  by  evaporation;  or  with  impure  material,  a 
preliminary  separation  may  bei<  effected  by  precipitating  the 
copper  as  cuprous  sulphide  in  the  following  manner. 

Moisten  5  grams  of  ore  with  10  c.c.  of  water,  add  10  c.c.  of 
nitric  acid  (d.,  1.42),  and  when  the  action  has  subsided,  10  c.c. 
more.  Digest  the  mixture  on  a  steam  bath  until  the  ore  is  de- 
composed and* the  sulphur  is  clean,  then  boil  for  a  few  minutes, 
cool  a  little,  and  add  10  c.c.  of  sulphuric  acid  (d.,  1.84).  Evapo- 
rate on  a  hot  plate  until  the  first  acid  is  expelled  and  white 
fumes  are  evolved.  Cool,  add  150  c.c.  of  water  and  10  c.c.  of 
sulphuric  acid.  If  silver  is  present,  precipitate  all  of  it  with 
sodium  chloride,  boil,  filter,  wash  the  residue  with  hot  water, 
dilute  to  300  c.c.,  and  heat  to  boiling. 

To  the  boiling  liquid,  add,  drop  by  drop,  a  saturated  solution 
of  sodium  thiosulphate.  The  ferric  iron  will  be  rapidly  reduced, 
and  when  colorless,  the  copper  will  begin  to  separate  as  cuprous 
sulphide.  The  point  at  which  this  begins  is  easily  seen.  Add 
about  2  c.c.  of  thiosulphate  after  the  copper  sulphide  begins  to 
form,  and  boil  until  the  sulphide  agglomerates.  Filter  the  hot 
solution  and  wash  with  hot  water,  or  better,  hydrogen  sulphide 
water.  Dry  and  ignite  in  a  No.  2  round-bottomed  porcelain 
crucible.  Moisten  the  residue  with  3  c.c.  of  water,  add  6  c.c. 
of  nitric  acid,  and  digest  for  a  few  minutes;  finally,  boil, 
transfer  the  liquid  to  a  tall  beaker  and  electrolyze  for  8  hours 
or  more,  according  to  the  per  cent  of  copper,  using  a  current  of 
.25  ampere  for  cylinders  5.5  cm.  wide  by  3.8  cm.  in  height. 
A  better  deposit  is  produced  by  adding  10  c.c.  of  sulphuric 
acid  also. 

The  Thiocyanate  Separation  of  Copper.  —  This  modification  is 
similar  to  the  titration  method  (3),  or  the  western  method  for 
slags,  and  where  antimony  is  present,  is  preferable  to  the  thio- 
sulphate, which  causes  the  deposition  of  at  least  a  part  of  the 
antimony.  According  to  A.  M.  Smoot,  treat  5  grams  of  the  ore 
as  above,  until  the  filtered  solution  from  the  insoluble  residue  has 
been  obtained.  Add  ammonia  until  the  liquid  is  alkaline  and 
then  make  acid  with  hydrochloric  acid,  leaving  an  excess  of 
about  1  c.c.  more  than  is  necessary  to  dissolve  the  iron  hydroxide. 
Dilute  to  300  c.c.,  add  50  c.c.  of  a  saturated  solution  of  sulphur 


64  ANALYSIS  OF  COPPER 

dioxide,  and  heat  on  a  steam  bath  until  the  iron  is  reduced. 
Add  3  to  5  c.c.  of  a  solution  of  potassium  thiocyanate  (150  grams 
to  1000  c.c.)  and  heat  again  until  the  precipitate  settles.  Filter 
through  double  papers,  wash  with  warm  2  per  cent  solution  of 
ammonium  nitrate,  and  proceed  as  in  the  thiosulphate  method. 
Compare  Western  method  for  slags  (5). 

9.  Roasted  Ores,  Iron  Oxides,  and  Cinders  usually  contain 
copper  which  is  insoluble  in  acids,  even  after  prolonged  digestion. 
Digest  3  grams  of  such  ores  with  25  c.c.  hydrochloric  acid  until 
the  iron  oxide  is  partly  dissolved,  then  add  10  c.c.  nitric  and 
boil  until  only  about  5  c.c.  remains.     Cool,  add  5  c.c.  sulphuric 
acid,  and  evaporate  until  SO3  fumes  are  given  off.     Cool,  add 
100  c.c.  of  water  or  more,  and  boil  until  all  soluble  salts  are 
dissolved.    Add  sodium  chloride,  if  necessary;  filter  and  wash  the 
residue  with  hot  water.     Transfer  the  residue  to  a  porcelain 
crucible;  dry,  ignite,   and  fuse  it  with  potassium  pyrosulphate. 
Dissolve  the  fusion  in  hot  water  and  filter  it  into  the  main  solu- 
tion;   or,  if  the  insoluble  copper  is  small,  as  is  usually  the  case, 
estimate  it  separately,  colorimetrically.     Filter  the  ammoniacal 
solution  through  asbestos,  and  read  the  color  in  100  c.c.  tubes, 
according  to  method  4b. 

9a.  D.  J.  Demorest  claims  that  a  precipitation  as  sulpho- 
cyanate  in  ammonium  tartrate  gives  a  more  complete  separa- 
tion from  antimony,  arsenic,  or  bismuth,  than  is  possible  in 
sulphuric  acid  alone.  If  electrolysis  is  preferred  to  titration,  the 
precipitate  as  obtained  is  dissolved  by  repeated  treatment  on 
the  filter,  in  a  covered  funnel,  with  18  c.c.  of  nitric  acid  (1:2), 
after  which  the  liquid  is  boiled  5  minutes  under  a  hood  to  de- 
stroy all  the  cyanogen  compounds  before  electrolysis.  (See  3a.) 

10.  Eastern  Methods  for  Mattes  are  the  same  as  those  for 
Western  mattes  already  described.    One  hundred  per  cent  copper 
foil  is,  however,  adopted  for  standards.     An  operator  is  justified 
in  using  any  one  of  methods  5,  6,  7,  8,  9,  that  is  best  adapted 
to  the  material  treated  and  the  commercial  requirements. 

11.  Copper  by  Electrolysis  in  Mansfeld  Ores.  —  For  the  assay 
of  about  800  shale  samples  per  month,1  this  method  is  said  to 
offer  the  advantage  that  it  permits  the  electrolysis  of  the  un- 
filtered  liquid  for  copper,  the   liquid  only  clarifying  by  long  set- 
tling.    The  procedure  is  as  follows:  —  A  sample  of  2  grams  of 

1  H.  Koch,  personal  communication. 


COPPER  IN   ORES  AND  FURNACE  PRODUCTS  65 

the  fine  powdered  shale  is  burned  at  a  dark  red  heat,  in  a  small 
porcelain  crucible  in  a  Plattner's  assay  muffle,  in  order  to  drive 
off  the  bitumens.  The  roasted 'mass  is  transferred  to  a  150  c.c. 
beaker,  20  c.c.  of  a  mixture  of  equ&l  parts  of  nitric  acid  (d.,  1.42) 
and  sulphuric  (d.,  1.2)  are  added  and  the  mixture  evaporated 
to  dry  ness  on  the  sand  bath.  The  cooled  mass  is  taken  up  in 
about  70  c.c.  of  a  diluted  nitric  acid  (1:7)  with  the  addition  of 
a  few  drops  of  sulphuric  acid.  The  electrolytic  precipitation  of 
the  copper  follows  without  filtration,  employing  a  small  platinum 
cylinder  of  66  sq.  cm.  total  area,  .and  a  small  platinum  wire 
spiral  as  anode.  As  finally  placed,  the  flat  spiral  wire  stands 
horizontally  without  touching  the  glass;-  the  cylinder  is  fastened 
to  a  special  tripod  stand. 

The  electrolyses  of  shales  are  ordinarily  arranged  as  a  set  of 
16  assays  to  one  working  stand,  or  rack,  the  strength  of  current 
being  .1  ampere  per  assay.  When  connected  at  evening,  the 
extraction  of  the  copper  proceeds  without  attention.  In  the 
morning,  the  assay  glass  is  washed  with  water  and  the  assayer 
notes  whether  any  copper  deposits  on  the  newly  moistened  por- 
tion of  the  cathode.  If  this  is  not  the  case,  the  cylinder  is  quickly 
withdrawn  from  the  solution,  then  washed  off  with  water  and 
alcohol,  dried  in  an  air  bath  at  90°  C.,  and  weighed  on  the 
balance.  (A  color  test  by  hydrogen  sulphide  is  a  more  certain 
indication  of  the  end-point  than  the  one  above  described.) 

Raw  Mansfeld  Ores.  —  With  ore  samples  from  the  deep  mines 
2  grams  are  evaporated  in  a  14  cm.  casserole  on  a  sand  bath, 
with  30  c.c.  nitric  acid  (d.,  1.2)  and  20  c.c.  sulphuric  acid  (d.,  1.2) 
the  heat  being  raised  so  that  the  separated  sulphur  burns. 
The  residue  is  taken  up  with  about  100  c.c.  water  and  10  c.c. 
of  sulphuric  acid,  and  then  4  c.c.  of  a  normal  solution  of  hydro- 
chloric acid  is  added  for  the  separation  of  silver.  After  standing 
12  hours,  the  liquid  is  passed  through  an  ordinary  8  cm.  filter 
into  a  beaker  15  cm.  high  and  8  cm.  wide,  washed  with  water, 
and  a  few  drops  of  sulphuric  acid  added  to  render  the  lead  in- 
soluble. The  electrolysis  of  the  filtrate  (after  the  addition  of 
20  c.c.  nitric  acid  and  dilution  to  400  c.c.)  is  carried  out,  gener- 
ally at  night,  with  the  aid  of  the  platinum  electrodes  already 
described,  and  with  a  current  of  .3  ampere  for  each  assay.  For 
the  estimation  of  Zn,  Ni,  and  Co,  in  ^his  material,  refer  to  a 
later  method  (3,  Chapter  VII). 


66  ANALYSIS  OF  COPPER 

Typolite  Ore.  —  This  is  treated  like  ordinary  ore  (q.  v.)  with 
the  exception  of  a  larger  addition  (8  c.c.)  of  yi^  normal  hydro- 
chloric acid,  on  account  of  the  higher  silver  contents.  An  excess 
of  the  acid  in  this  case  must  be  carefully  avoided,  or  the  copper 
will  deposit  in  a  spongy  form.  Current,  .3  ampere  per  assay. 

12.  Desilverized  Residues.  —  In  this  oxidized  product,  con- 
taining about  70  per  cent  copper,  it  is  not  necessary  to  treat  in 
a  casserole,  to  burn  off  sulphur,  etc.    Two  grams  are  digested  with 
60  c.c.  nitric  acid  and  10  c.c.  concentrated  sulphuric  acid  until 
a  white  anhydrous  deposit  of  copper  sulphate  is  formed.     After 
dilution  with  water  to  about  400  c.c.,  10  c.c.  ammonia  is  added 
to  lessen  the   acidity,  and  the  acid   liquid  electrolyzed  with  .4 
ampere.     The  assays  are  usually  combined  in  sets  of  3  to  4, 
but  the  samples  must  be  similar  to  insure  an  equal  division  of 
current. 

13.  Mansfeld  Ore  Slags.  —  Five  grams  of  powdered  slag  are 
mixed  in  a  casserole  with  30  c.c.  of  nitric  acid  and  15  c.c.  of 
sulphuric   acid    and    evaporated   to    dry  ness    on    a   sand    bath. 
It  has  been  proved   that  chilled    slag  is   quickly  decomposed, 
while    stiff-tempered    slag    (i.e.,    gradually    cooled)    requires    an 
alkali  melt.     The  dry  residue  is  treated  hot  with  100  c.c.  water 
and  10   c.c.  sulphuric   acid,  then   filtered   through  an   ordinary 
12  cm.  paper  into  a  beaker  (15  by  8   cm).    The   filtrate,  after 
adding  20  c.c.  nitric  acid,  is  electrolyzed  with  platinum  electrodes 
and  a  current  of  0.11  ampere  per  assay. 

14.  Typolite  Slags.  —  Two  grams  are  evaporated  to  dryness 
with  30  c.c.  aqua-regia  and  15  c.c.  sulphuric  acid.  The  residue 
is  extracted  with  100  c.c.  of  water  and  10  c.c.  sulphuric  acid. 
The  solution,  after  warming,  is  filtered  into  a  beaker. 

Twenty  c.c.  nitric  acid  are  added  to  the  filtrate  which  is 
then  treated  with  a  few  drops  of  cold  saturated  oxalic  acid  in 
order  to  overcome  the  harmful  effect  of  the  heavy  iron  contents 
of  this  material  (40  per  cent  Fe) .  Tests  are  arranged  in  sets  with 
a  current  of  .3  ampere  per  assay.  The  routine  electrolyses  are 
carried  on  over  night.  It  is  only  in  urgent  cases  that  the  process 
is  finished  in  the  daytime  at  the  sacrifice  of  accuracy,  in  which 
case  the  liquids  are  warmed  to  40  to  45°  C.  The  author  con- 
siders that  as  the  local  conditions  require  a  simple  assay,  the  use 
of  mechanical  stirrers  is  prohibited. 

Magnetic  Separation.  —  The  original  ore  is  peculiar  to  the 


COPPER  IN  ORES  AND  FURNACE  PRODUCTS  67 

district.  A  description  of  the  slag  produced  has  been  necessarily 
condensed  in  the  translation  of  the  original  paper.  Most  of  the 
copper  contents  exist  in  such  felag  in  metallic  form.  Some  sul- 
phide and  silicate  are  also  present,  hence  it  is  erroneous  to  report 
all  the  copper  as  metal.  Magnetic  separation  has  accordingly 
been  taken  up  for  the  successive  mechanical  division  of  the 
copper,  as  metal  and  sulphide,  from  the  silicates.  Magnetic 
treatment  is  very  efficient  in  consequence  of  the  considerable 
proportion  of  magnetic  oxide  of  iron.  By  a  small  electro- 
magnet, connected  with  six  Meidinger  elements,  pieces  of  nut 
size  are  attracted  with  ease.  The  separation  can  be  only 
approximate  as  the  slag  grains  will  inclose,  or  be  covered 
with,  non-magnetic  particles.  Nevertheless,  four  treatments  of 
typolite  slag  (containing  7.75  per  cent  copper  and  .161  per  cent 
sulphur)  yielded  15.9  per  cent  of  non-magnetic  residue  which 
assayed  nearly  33.8  per  cent  metallic  copper  and  3.48  per 
cent  copper  sulphide. 

Method  of  Assay.  —  The  total  copper  is  determined  by  the 
usual  methods.  For  the  valuation  of  the  metallic  copper  only, 
the  most  suitable  method  is  the  extraction  of  powdered  slag  with 
standard  solution  of  silver  nitrate,  followed  by  the  dry  assay  of 
the  silver  precipitated  by  the  copper;  and  as  a  control,  the 
titration  of  the  silver  remaining  in  the  solution  by  potassium 
thiocyanate  after  the  Volhard  method.  The  copper  sulphide  and 
the  metallic  iron  present  (perhaps  1.25  per  cent)  also  take  full 
part  in  the  reaction  of  the  silver  nitrate  with  the  metallic  copper 
and  only  the  silicate  remains,  so  that  the  relative  proportions  of 
copper  metal,  sulphide,  and  silicate  are  easily  calculated.  For 
a  total  of  7.75  per  cent  as  noted  above,  about  6.85  per  cent 
would  exist  as  metal,  .58  per  cent  as  sulphide,  and  .32  per  cent 
as  silicate. 

NOTE  1 .  —  The  magnetically  separated  copper  is  itself  argen- 
tiferous. It  carries  the  silver  excess  of  the  original  typolite  slag 
and  a  notable  amount  of  gold  even  after  skimming  off  some  half- 
melted  ore  which  floats  on  the  slag  in  the  descending  series  of 
skimming  pots  at  the  furnace.  The  slag  copper  is  enriched  with 
the  whole  nickel  content  of .  the  ore,  and  copper  bottoms  are 
formed  at  the  same  time  in  the  pots.  When  this  same  slag  is, 
however,  remelted  in  a  furnace  with  regulus,  the  magnetic  sepa- 


68  ANALYSIS  OF  COPPER 

ration  of  the  ground  slag  is  hardly  profitable  in  spite  of  the  high 
iron  content  (nearly  38  per  cent),  for  the  reason  that  the  iron 
is  then  present  in  the  final  slag  as  non-magnetic  ferrous  silicate. 

NOTE  2.  —  When  typolite  slag  is  cooled  in  the  series  of  pots, 
it  forms  zones  or  layers  which  increase  in  magnetic  iron  oxide 
towards  the  bottom  and  consequently  increase  in  electrical  con- 
ductivity. If  the  upper  zone  contains  1  to  3  per  cent  copper 
and  0  to  .003  per  cent  silver,  the  middle  will  be  twice  as  rich  while 
the  lowest  zone  will  show  4.5  to  5.4  per  cent  copper  and  .015 
to  .017  per  cent  silver.  It  was  proved  by  a  series  of  tests  that 
it  is  impossible  to  obtain  a  proper  average  by  ladle  samples  from 
the  settling  pots. 


CHAPTER  V 
ANALYSIS  OF  ORES,   SLAGS,   MATTE,  AND  FLUE  DUST 

CONTROL  OF  SMELTING  FURNACES 

THE  methods  described  in  this  chapter  include  only  the 
determinations  ordinarily  required  to  furnish  the  data  to 
metallurgists  for  regular  daily  control  of  furnace  operations. 
Occasional  tests  for  arsenic,  bismuth,  nickel,  sodium,  and  rarer 
elements,  are  reserved  for  Chapters  VI  and  VII.  The  methods 
of  this  chapter  are  arranged  in  the  sequence  adopted  in  practical 
work,  rather  than  in  alphabetical  order. 

Classification.  —  Furnace  material,  for  the  purposes  of  analy- 
sis, may  be  divided  into  two  classes :  —  First,  material  decomposed 
by  acids,  such  as  chilled  blast  furnace  slags;  second,  refractory 
material,  leaving  an  insoluble  residue  after  acid  treatment;  for 
example,  reverberatory  slags,  calcined  ores,  and  flue  dust.  Such 
a  residue  evidently  requires  fusion.  The  methods  are  those  of 
the  largest  western  reduction  works,  except  in  cases  where  other 
methods  are  specified. 

DETERMINATION   OF  INSOLUBLE  MATTER 

1.  In  Raw  Ores.  —  For  a  special  test  on  Butte  ores,  refer  to 
the  method  for  sulphur  (16).  As  a  general  method,  heat  a  half- 
gram  sample  in  a  small  beaker,  or  casserole,  for  ten  minutes 
with  10  c.c.  of  hydrochloric  acid,  add  1  to  5  c.c.  of  nitric  acid 
(depending  on  the  sulphides  present),  cover  with  a  watch  glass 
until  violent  action  ceases,  then  uncover  and  evaporate  to  dry- 
ness  on  the  steam  bath.  Sulphides  may  be  treated  with  5  c.c. 
of  nitric  acid  and  a  little  potassium  chlorate,  10  c.c.  of  hydro- 
chloric acid  added  when  the  action  becomes  quiet,  and  the 
liquid  evaporated  to  dry  ness  as  before.  When  dry,  remove  from 
the  bath,  add  15  c.c.  of  hydrochloric  acid  and  50  c.c.  of  hot 
water.  Bring  to  boiling  and  filter.  Wash  the  insoluble  matter 
with  dilute  (1:9)  hydrochloric  acid,  then  with  boiling  water. 


70  ANALYSIS  OF  COPPER 

Fold  the  filter  about  the  " insoluble,"  ignite,  and  weigh.  This 
assay  may  be  combined  with  the  iron  titration. 

Another  operator  1  recommends  a  first  treatment  with  7  to  10 
c.c.  of  nitric  acid,  followed  by  evaporation  to  dryness,  and  cooling. 
Then  add  30  c.c.  of  (1:1)  hydrochloric  acid  and  heat  until  the 
solution  is  as  complete  as  possible.  In  presence  of  carbonaceous 
matter,  it  may  be  necessary  to  bake  for  a  long  time,  as  such 
residues  hold  acid  very  tenaciously. 

Roasted  Ores.  —  Digest  with  hydrochloric  acid,  without  boil- 
ing, until  the  oxidized  part  is  dissolved,  add  about  3  c.c.  of 
nitric  acid  to  decompose  sulphides,  and  dry  as  before. 

Barium  Sulphate  Ores.  —  Treat  with  10  c.c.  of  hydrochloric 
acid  (1:  1),  boil  a  few  minutes,  add  4  to  5  c.c.  of  nitric  acid, 
and  after  action  has  ceased,  dry  and  bake,  then  proceed  as 
already  indicated.  After  the  " total  insoluble  matter"  is  weighed, 
fuse  it  with  sodium  carbonate,  or  mixed  carbonates,  8  parts  to 
1  of  residue,  digest  the  fusion  with  water  until  disintegrated, 
filter,  and  wash.  Wash  out  the  crucible*  with  5  c.c.  of  hydro- 
chloric acid  (1:  1)  and  with  this  acid  dissolve  the  residue  upon 
the  filter,  being  careful  that  it  is  all  dissolved  and  the  filter 
washed  out  clean.  Precipitate  the  barium  as  sulphate  from  a 
boiling  solution,  and  deduct  this  barium  sulphate  from  the 
"total  insoluble"  to  obtain  a  result  defined  by  custom  as  "the 
insoluble  residue." 

SILICA 

2.  In  Chilled  Blast  Furnace  Slags.  —  To  .5  gram  of  slag  in 
a  small  porcelain  casserole,  add  six  drops  of  water  and  about 
3  c.c.  of  strong  hydrochloric  acid.  Stir  well  with  a  glass  rod 
until  all  lumps  are  broken  up  and  a  smooth  jelly  results.  Now 
add  a  few  drops  of  nitric  acid  and  work  the  jelly  up  and  around 
the  sides  of  the  casserole  to  a  height  of  about  1.2  cm.  This  will 
permit  of  very  rapid  dehydration,  and  will  reduce  the  loss  by 
"spitting."  Place  the  casserole,  uncovered,  upon  the  plate  and 
evaporate  off  all  traces  of  acids,  care  being  taken,  however,  not 
to  prolong  the  baking  at  too  high  a  temperature,  or  some 
alumina  will  unite  with  the  silica  and  give  too  high  a  result 
when  the  direct  weight  of  silica  is  taken;  the  residue,  after 
ignition,  being  of  a  gray  instead  of  a  white  color. 

1  Western  Chem.  and  Met.  3,  120. 


ORES,   SLAGS,   MATTE,   AND  FLUE  DUST  71 

Slightly  cool  the  casserole,  add  about  20  c.c.  of  hydrochloric 
acid  (d.,  1.20),  and  boil  for  a  few- minutes.  Dilute  with  a  little 
hot  water  and  filter  while  hot,  Cashing  well  with  hot  water 
until  free  from  chlorides:'  Ignite  and  weigh  as  silica.  If  exact 
results,  or  the  percentage  of  true  silica  is  required,  additional 
precautions  are  taken  as  stated  in  the  paragraphs  on  ores. 

In  a  statement  of  a  "co-operative  analysis,"  Thorn  Smith1 
has  indicated  a  necessary  precaution.  At  least  two  evaporations 
to  hard  dryness  with  an  intermediate  filtration  are  required  to 
render  precipitated  silica  insoluble  in  dilute  acids.  When  ac- 
curate work  is  attempted,  the  silica  should  finally  be  ignited 
ten  minutes  with  the  blast  lamp. 

It  is  also  necessary  to  correct,  in  such  work,  for  the  small 
amounts  of  oxides  of  iron  or  alumina,  and  sulphates  of  alkaline 
earths,  which  remain  after  treatment  of  the  silica  with  sulphuric 
acid  and  excess  of  hydrofluoric  acid. 

The  manner  of  calculation  of  this  correction  to  the  original 
weight  of  siliceous  residue  depends  on  the  forms  in  which  the 
bases  may  be  assumed  to  exist  in  the  ignited  siliceous  residue. 
Platinum  dishes  are  best  suited  to  accurate  work  in  complete 
analysis  of  a  slag  or  ore. 

Solubility  of  Jena  Glass.  —  Thorn  Smith  and  A.  M.  Smoot 
have  proved  that  Jena  glass,  although  heat  resistant,  is  easily 
attacked  by  alkalies.  This  undesirable  property  is  due  to  the 
presence  of  oxides  or  silicates  of  zinc  as  a  constituent. 

Special  Solvents.  —  For  complete  solution,  Smith  decomposes 
Tennessee  cupola  slags  by  digestion  in  a  platinum  dish  with  a 
mixture  of  hydrofluoric  acid  and  nitric  acid.  To  dissolve  the 
slag  for  an  iron  titration  only,  hydrochloric  is  substituted  for 
nitric  acid. 

Another  solvent  used  for  ores  and  slags  is  the  "  chlorate 
mixture"  (1  part  sulphuric  acid,  1  part  nitric,  and  1  part  of  a 
saturated  solution  of  potassium  chlorate  in  nitric  acid). 

3.  In  Lake  Superior  Slags.  —  Waste  cupola  slags  are  chilled 
by  granulation  in  water  at  the  furnace,  the  sample  dried,  then 
crushed  and  divided  to  obtain  a  25-  to  50-gram  sample  for  assay 
which  will  pass  a  sieve  of  100  meshes  to  the  linear  inch  (39  per 
cm.).  The  copper  prills,  remaining  on  the  sieve,  are  separately 

1  Eng.  and  Min.  Jour.  75,  295.  W.  F.  Hillebrand,  J.  Am.  Chem.  Soc.  24, 
362.  Bull.  422,  U.  S.  Geol.  Survey. 


72  ANALYSIS  OF  COPPER 

weighed.  In  accurate  complete  analysis,  the  free  iron  is  esti- 
mated by  magnetic  separation  according  to  the  principle  outlined 
in  Chapter  II,  under  "  Correction  for  iron  from  grinder."  In 
some  slags  this  iron  contains  copper.  The  total  copper  is 
determined  most  rapidly  by  method  6,  Chapter  IV,  but  may  also 
be  estimated  in  the  filtrate  from  the  silica. 

Silica.  —  Dissolve  2  grams  of  slag  in  a  300  c.c.  casserole 
by  boiling  with  a  mixture  of  15  c.c.  distilled  water,  15  c.c. 
strong  nitric  acid,  and  10  c.c.  of  sulphuric  acid  (d.,  1.84)  until 
white  fumes  appear  and  the  residue,  when  gently  rubbed,  has 
become  a  smooth  paste.  Partially  cool  the  residue,  then  add 
90  c.c.  of  distilled  water,  wash  the  glass  cover  and  replace 
it.  Boil  for  a  few  minutes  until  the  soluble  matter  is  dis- 
solved, transfer  to  an  electrolytic  beaker,  and  place  on  the 
battery  stand  for  the  estimation  of  copper  unless  silica  is 
the  only  constituent  to  be  determined,  in  which  case  the 
solution  is  filtered  at  once. 

For  direct  estimation  of  silica,  boil  the  residue  with  75  c.c.  of 
(1:2)  hydrochloric  acid,  decant  through  an  11  cm.  filter  placed 
in  a  platinum  cone  over  a  suction  flask.  Then  boil  the  residue 
with  50  c.c.  of  (1:1)  hydrochloric  acid  to  extract  calcium  sul- 
phate, dilute  to  75  c.c.,  filter,  wash,  ignite,  and  weigh.  Treat 
the  residue  with  hydrofluoric  acid  and  one  drop  of  sulphuric  after 
moistening  with  water.  Ignite  and  re  weigh.  Fuse  with  potas- 
sium pyrosulphate,  dissolve,  and  add  to  main  solution.  If  a  test 
for  barium  is  advisable,  separate  it  from  the  original  residue  by 
fusion  with  sodium  carbonate  amd  proceed  as  in  method  1,  under 
the  head  of  "Barium  Sulphate  Ores." 

SILICA  IN  REFRACTORY  MATERIALS 

4.  In  Reverberatory  Slags  (also  Calcines,  Briquettes,  and 
Flue  Dust).  —  Such  material  yields  an  insoluble  residue  requir- 
ing fusion.  Reverberatory  furnace  slag,  from  smelting  of  ores, 
contains  such  a  small  amount  of  copper  that  it  can  be  fused 
without  any  preliminary  treatment. 

With  other  refractory  products,  weigh  .5  gram,  place  in  a 
small  casserole,  and  add  6  c.c.  of  hydrochloric  acid  and  3  c.c.  of 
nitric  acid.  Cover  the  casserole,  heat  for  a  few  minutes  on  the 
hot  plate,  bring  to  boiling,  dilute  with  boiling  water,  and  filter 


ORES,  SLAGS,  MATTE,  AND  FLUE  DUST  73 

through  a  fine  paper  into  a  larger  casserole.  Wash  the  residue 
on  the  paper  three  times.  Fold  the  filter  about  the  residue  and 
ignite  it  in  a  cup  or  crucible.  Place  the  filtrate  on  a  hot  plate 
while  the  fusion  is  being  made.  To  fuse  the  slag  or  ignited 
oxides,  mix  them  well  with  6  to  8  grams  of  anhydrous  so- 
dium carbonate  in  a  platinum  crucible  (or  a  dish  if  preferred), 
and  then  cover  the  mixture  with  1  or  2  grams  of  sodium  car- 
bonate. Place  on  a  scorifier,  preferably,  and  fuse  in  a  muffle. 
Raise  the  heat  gradually  from  dull  to  bright  red,  and  keep  at  a 
red  heat  for  15  minutes.  Dip  the  crucible  in  water  to  cool. 
Partly  fill  with  water  and  warm  for  a  few  minutes  on  a  hot 
plate.  The  cake,  as  a  rule,  can  be  loosened  from  the  crucible 
by  this  treatment.  Wash  it  into  a  casserole  containing  the  main 
solution  which  has  already  been  evaporated  to  dryness.  Cover, 
then  add  10  to  30  c.c.  of  hydrochloric  and  1  c.c.  of  nitric  acid. 
If  the  fusion  was  made  in  a  dish,  cool,  add  water,  then  add  10 
c.c.  of  hydrochloric  acid  and  warm  until  the  contents  can  be 
easily  transferred  to  the  original  casserole.  If  the  color  of  the 
fusion  indicates  the  presence  of  much  manganese,  it  must  be 
removed  from  the  dish  without  the  use  of  acid,  as  there  is 
danger  of  liberation  of  chlorine. 

Evaporate  the  contents  of  the  casserole  to  complete  dryness 
again,  but  do  not  bake  long  above  115°  C.,  as  some  silica  is 
liable  to  recombine  with  the  alumina.1  When  dry,  remove  from 
plate,  add  10  c.c.  hydrochloric  acid  and  30  c.c.  of  water,  and 
boil  for  a  few  minutes.  Filter,  wash  ten  times,  ignite,  and 
weigh.  Test  the  residue  for  purity,  by  the  usual,  treatment 
with  hydrofluoric  acid,  and  ignition.  For  very  accurate  results 
increase  the  sample  weight. 

ALUMINA 

5.  Alumina  in  Ores  and  Slags.  —  Decompose  the  sample, 
dehydrate,  and  filter  off  the  silica  as  in  the  silica  determinations. 
Purify  the  silica  by  evaporation  with  a  drop  of  sulphuric  acid 
and  excess  of  hydrofluoric  acid  and  fuse  the  residue  with  a  little 
potassium  pyrosulphate,  if  necessary,  to  bring  it  into  solution. 
In  the  filtrates,  determine  the  alumina  by  the  Western  phosphate 
method,  to  be  described. 

1  Methods  of  Rock  Analysis,  by  W.  F.  Hillebrand;  also  J.  Am.  Chem. 
Soc.  24,  362,  and  Bull.  422,  U.  S.  GeoL  Survey. 


74  ANALYSIS  OF  COPPER 

Instead  of  treating  with  hydrogen  sulphide,  ferric  hydroxide 
and  alumina  may  be  precipitated  with  ammonia.  The  mass  is 
dissolved  in  hydrochloric  acid,  the  solution  diluted  to  400  c.c., 
and  the  alumina  precipitated  as  before.  This  serves  to  separate 
the  alumina  from  the  small  amount  of  copper  contained  in  such 
waste  ore  slags.  The  other  metals  affected  by  hydrogen  sulphide 
are  usually  present  in  such  small  quantities  that  they  may  be 
neglected.  In  making  the  ammonia  separation,  a  large  excess  of 
ammonium  chloride  must  be  present  and  the  solution  boiled  for 
fifteen  minutes  to  break  up  any  aluminates  which  may  have 
been  formed. 

Precipitation.  —  After  the  excess  copper  has  been  removed, 
dilute  the  acid  filtrate  from  the  silica  with  cold  water  to  about 
400  c.c.,  add  30  c.c.  of  a  10  per  cent  solution  of  ammonium 
phosphate,  and  then  dilute  ammonia  until  a  slight  permanent 
deposit  forms.  Now  add  1.5  c.c.  concentrated  hydrochloric  acid 
and  40  c.c.  of  a  20  per  cent  solution  of  sodium  thiosulphate  and 
heat  to  boiling.  When  boiling  has  continued  a  couple  of  minutes, 
add  15  c.c.  of  a  20  per  cent  solution  of  ammonium  acetate  and 
6  c.c.  of  strong  acetic  acid,  and  boil  about  15  minutes  longer. 
This  addition  of  ammonium  acetate  and  acetic  acid  after  boiling 
gives  a  much  more  granular  precipitate,  which,  after  allowing  it 
to  settle  for  about  20  minutes  and  decanting  the  clear  superna- 
tant fluid,  filters  very  rapidly.  Wash  with  hot  water  ten  times, 
dry,  ignite  gently  at  first,  and  weigh  as  A1203,  P2O5  —  41.85 
per  cent  of  which  is  alumina  (A^Oa). 

Instead  of  the  previous  method,  the  following  plan  may  be 
adopted  for  the  removal  of  the  copper  and  similar  metals. 
Should  metals  affected  by  hydrogen  sulphide  be  present,  add 
ammonia  to  the  filtrate  from  the  silica  until  the  liquid  is  nearly 
neutral,  then  add  2  or  3  c.c.  of  hydrochloric  acid  in  excess, 
reduce  the  solution  with  sodium  sulphite,  and  boil  off  the  excess 
of  sulphur  dioxide.  Add  15  c.c.  of  hydrochloric  acid,  pass 
hydrogen  sulphide  through  the  solution,  filter  off  and  wash  the 
sulphides  with  cold  water.  Boil  off  all  hydrogen  sulphide  from 
the  filtrate,  dilute  to  400  c.c.  with  cold  water,  and  proceed  as 

before. 

IRON   OXIDES 

6.  Direct  Titration  of  Ores.  —  Oxidized  iron  ores  (carrying 
copper)  often  dissolve  more  rapidly  if  a  little  stannous  chloride 


ORES,   SLAGS,   MATTE,   AND  FLUE  DUST  75 

is  added  with  the  hydrochloric  acid.  If  the  tin  solution  is  added 
to  aid  the  solution  of  the  iron?  then  the  reduction  of  iron  before 
titration  must  be  made  with  stajmous  chloride  (as  tin  interferes 
with  a  solution  reduced  with  lead),  or  an  excess  of  mercuric 
chloride  should  be  added  to  the  solution  after  decanting  from  lead. 

To  the  filtrate,  add  5  to  10  grams  of  test  lead  and  boil  until 
colorless.  Decant  from  the  lead  (filtration  often  being  neces- 
sary), and  wash  the  lead  very  thoroughly.  Cool,  add  10  c.c.  of 
hydrochloric  acid,  and  titrate  with  potassium  bichromate,  if 
preferred.  If  the  solution  appears  yellowish  after  decanting 
from  lead,  add  2  drops  of  stannous  chloride  solution  and  mer- 
curic chloride  in  excess  before  titration.  When  copper,  arsenic, 
and  antimony  are  absent,  heat  the  filtrate  from  "insoluble" 
nearly  to  boiling,  reduce  as  before,  cool,  and  titrate.  Separation 
of  iron  from  copper  by  ammonia  is  not  complete  in  one  treat- 
ment, however.  The  ferric  and  aluminum  hydroxides,  with  the 
filter,  are  placed  in  a  beaker,  50  c.c.  of  boiling  water  added,  and 
the  solution  titrated  as  already  described.  If  care  is  taken  not 
to  add  the  stannous  chloride  in  large  excess,  the  mercuric 
chloride  may  be  added  to  the  hot  liquid.  It  is  then  diluted 
with  cold  water  and  titrated.  If  a  large  excess  of  stannous 
chloride  is  added  by  accident,  run  in  potassium  permanganate 
solution  from  a  burette  until  the  iron  solution  is  a  pale  yellow; 
add  one  or  two  drops  stannous  chloride  in  excess,  then  mercuric 
chloride,  and  proceed  as  before. 

7.  Lake  Superior  Method.  —  Dissolve  2  grams  of  sample  in 
acids,  evaporate  to  fumes  with  10  c.c.  sulphuric  acid  and 
dilute.  (See  method  5,  Chapter  IV.)  Two  precipitations  of 
iron  by  ammonia  do  not  effect  a  complete  separation.  The 
copper  may  be  very  rapidly  and  exactly  removed  by  placing  the 
solution  in  an  electrolytic  beaker  (see  electrolytic  assay  of 
copper),  and  passing  3  to  4.5  amperes  of  current  through  the 
solution  after  placing  the  beaker  in  a  Frary  solenoid,  or  rotary 
device.  To  get  a  bright  deposit,  add  5  to  8  c.c.  nitric  acid 
and  keep  the  solution  cold.  When  testing  for  the  end-point  of 
electrolytic  deposition,  preserve  the  test  portion,  and  return  it 
to  the  main  solution  after  the  plate  has  been  withdrawn.  The 
sulphur  should  first  be  destroyed  by  heating  the  test  portion  with 
a  little  potassium  permanganate.  The  time  of  electrolysis  for  a 
2-gram  sample  is  30  to  60  minutes. 


76  ANALYSIS  OF  COPPER 

For  the  exact  estimation  of  iron  it  is  necessary  to  filter  the 
original  solution  (or  electrolyte)  and  decompose  the  washed 
insoluble  matter  by  fusion.  Combine  the  two  solutions,  oxidize 
the  iron,  precipitate  twice  with  ammonia,  redissolve  the  iron  in 
10  c.c.  hydrochloric  acid  (1:1),  and  wash  the  paper.  Reduce  as 
above,  destroying  the  slight  excess  of  stannous  chloride  by  the 
addition  of  5  c.c.  of  a  saturated  solution  of  mercuric  chloride. 
Dilute  to  400  to  500  c.c.  and  titrate  with  potassium  perman- 
ganate (39,  Chapter  III).  Add  10  to  20  c.c.  of  titrating  solution 
25  to  prevent  the  formation  of  a  yellow  iron  coloration.  One 
c.c.  of  permanganate  oxidizes  about  .01  gram  of  iron,  Fe. 

If  a  test  of  the  electrolyte  is  to  be  made  for  iron  only,  it  may 
be  evaporated  to  fumes  to  remove  nitric  acid. 

Add  30  c.c.  of  water  and  10  of  hydrochloric  acid,  heat  to 
boiling,  then  add  sufficient  potassium  permanganate  to  produce 
a  yellow  color  and  destroy  a  trace  of  sulphur.  Reduce  as  before 
and  titrate,  after  dilution  with  cold  water  to  400  c.c.  Calculate 
to  the  compound  in  which  the  iron  exists  in  the  ore. 

8.  Iron  in  Slags.  —  The  percentage  of  iron  oxide,  FeO,  is 
found  by  titration  of  a  0.5  to  2  gram  sample.  Chilled  waste  slags 
from  Lake  Superior  furnaces  may  be  dissolved  as  directed  in 
method  3  for  silica,  and  the  copper  removed  by  rapid  electrolysis. 
Boil  the  solution  down  to  white  fumes  after  electrolysis  to  re- 
move nitric  acid. 

Add  30  c.c.  of  water  and  10  c.c.  of  hydrochloric  acid,  heat  to 
boiling,  and  add  a  little  potassium  permanganate,  if  necessary,  to 
color  the  solution  yellow  and  destroy  any  sulphur  compound. 
Reduce  and  titrate  as  with  ores.  For  ordinary  furnace  tests  it 
is  not  necessary  to  remove  the  copper.  Proceed  as  in  the  next 
paragraph. 

Ore  slags,  from  the  blast  furnace,  are  dissolved  in  a  similar 
manner.  To  .5  or  1  gram  of  slag  in  a  beaker,  add  about  50  c.c.  of 
boiling  water,  and  then  while  stirring  to  keep  the  slag  in  suspen- 
sion, pour  in  10  to  15  c.c.  of  hydrochloric  acid  (d.,  1.2).  Boil 
for  a  few  minutes  until  the  solution  clears  (any  slight  residue  of 
coke  dust  being  neglected).  Oxidize  to  yellow  color  with  per- 
manganate. Reduce  with  stannous  chloride  in  very  slight  excess, 
followed  by  mercuric  chloride  in  excess  as  already  mentioned  in 
6,  and  titrate  with  either  potassium  bichromate,  or  permanga- 
nate, as  preferred. 


ORES,   SLAGS,   MATTE,   AND  FLUE  DUST  77 

With  the  dichromate,  use  potassium  ferricyanide  as  an  indi- 
cator, placing  the  test  portions  in  contact  on  a  white  spot  plate. 

t 

CALCIUM  ANQ<  MAGNESIUM 

9.  Direct    Method    for    Lime.  —  Precipitation    of    calcium 
oxalate  in  oxalic 'acid  solution,  in  presence  of  the  other  bases,  is 
used  in  the  western  States  as  a  special  test  for  lime  only. 

To  the  filtrate  from  the  silica,  add  ammonia  in  excess  and 
then  oxalic  acid,  little  by  little,  until  the  hydroxides  just  dis- 
solve. Make  the  solution  slightly  alkaline  once  more,  and  then 
redissolve  the  iron  by  adding  oxalic  acid  in  slight  excess.  The 
solution  should  now  be  of  a  light  apple-green  color.  Boil  well 
for  a  few  minutes,  filter,  and  wash  well  with  hot  water  until 
free  from  oxalic  acid,  —  six  or  seven  times  usually  being  sufficient. 
Drop  the  filter  and  calcium  oxalate  into  a  beaker  containing  150 
c.c.  of  boiling  water.  Add  10  c.c.  of  dilute  (1:1)  sulphuric  acid 
and  titrate  at  once  with  potassium  permanganate  (solution  40, 
Chapter  III).  The  permanganate  may  be  standardized  with 
chemically  pure  sodium  oxalate  which  should  be  dried  at  100° 
C.  before  use  and  preserved  in  a  small  glass-stoppered  bottle. 
Na2C2O4  x  .41843  =  CaO.  Correct  sodium  oxalate  may  be  ob- 
tained from  the  U.  S.  Bureau  of  Standards. 

10.  Calcium  and  Magnesium  (in  chilled  cupola  slags) .  —  To 
the  filtrate  from  a  silica  determination  add  an  excess  of  ammonia 
and  5  grams  of  ammonium  chloride  (prepared  from  chemically 
pure  reagents),  then  10  c.c.  of  bromine  water  and  about  .1  gram 
of  ammonium  persulphate,  as  in  the  "Estimation  of  zinc,"  15, 
Chapter  VII.     Bring  to  a  boil,  filter,  dissolve  the  precipitate  in 
dilute   hydrochloric   acid,    add   bromine   water   and   ammonium 
persulphate  as  before,  heat  to  boiling  and  filter  again. 

After  washing  the  hydroxides,  precipitate  the  calcium  (in  the 
combined  filtrates  from  iron,  alumina,  and  manganese),  with 
ammonium  oxalate,  using  .5  to  1  gram  of  the  dry  salt  or  20 
c.c.  of  the  saturated  solution.  Filter,  wash  well,  and  in  the 
filtrate,  separate  the  magnesia  by  stirring  five  minutes  with  an 
excess  of  ammonium  phosphate  (6  and  51,  Chapter  III).  Have 
the  solution  strongly  ammoniacal  with  about  one-fourth  its 
volume  of  ammonium  hydroxide  (d.,  .90)  to  prevent  the  pre- 
cipitation of  zinc.  Dissolve  the  precipitate  in  a  very  small 
amount  of  hydrochloric  acid,  add  a  small  crystal  of  the  phos- 


78  ANALYSIS  OF  COPPER 

phate,  then  ammonia  drop  by  drop,  until  alkaline,  stirring 
vigorously.  Wash  with .  dilute  ammonium  hydroxide  (1 :10) 
containing  10  per  cent  of  ammonium  nitrate,  ignite  gently  at 
first,  and  weigh  when  cooled.  Magnesium  pyrophosphate, 
Mg2P2C>7,  x  0.36207  equals  magnesium  oxide,  MgO. 

In  the  absence  of  manganese,  omit  the  bromine  water  and 
persulphate.  In  some  Lake  Superior  slags  which  contain  much 
lime,  the  calcium  oxalate  should  be  dissolved  and  reprecipitated 
to  obtain  a  perfect  separation  from  magnesium  salts.  About  75 
c.c.  of  water  and  5  c.c.  of  sulphuric  acid  are  finally  used  to 
dissolve  the  calcium  oxalate  for  titration.  Place  the  filter  and 
contents  in  the  original  beaker,  cover  with  the  dilute  acid,  and 
heat  nearly  to  boiling.  A  few  drops  of  manganous  sulphate  in 
the  solution  causes  the  permanganate  to  act  more  quickly. 

11.  Calcium  and  Magnesium  (in  reverberatory  slags  and  ores). 
—  Precipitate  hydroxides  with  ammonium  hydroxide  and  wash  six 
times,  then  dissolve  in  dilute  hydrochloric  acid  and  titrate  the  iron. 

The  calcium  oxide  in  these  refractory  samples  is  usually 
below  6  per  cent,  and  only  .2  to  .4  per  cent  of  calcium  oxide 
would  be  recovered  by  redissolving  and  reprecipitating  the 
hydroxides.  With  higher  percentages,  a  second  separation  with 
ammonia  must  be  made  even  in  routine  technical  work.  Rich 
oxidized  slags  from  Lake  Superior  furnaces  treating  concentrates 
of  native  copper,  often  contain  as  much  as  5  per  cent  of  free 
shot  copper  which  must  be  separated  and  weighed  during  the 
grinding  and  sizing  of  the  25-  to  50-pound  sample.  The  insoluble 
portion  of  the  slag  is  fused,  preparatory  to  analysis  for  bases. 
After  the  slag  has  been  totally  decomposed  with  the  exception 
of  silica,  the  bases  are  determined  as  customary  with  blast 
furnace  slags. 

Magnesium  is  determined  by  precipitation  with  phosphates, 
as  in  (10). 

12.  Sodium  and  Potassium  Oxides.  —  The  determination  of 
these  elements  is  seldom  necessary  in  furnace  control.     Refer  to 
Chapter  VII  (6,  7,  9). 

SULPHUR  IN   CRUDE   PRODUCTS 

Principle.  —  Sulphur,  or  sulphate,  is  usually  estimated  by 
oxidizing  the  sulphur  to  sulphuric  acid,  then  precipitating  with 
barium  chloride  in  a  pure  hydrochloric  acid  solution. 


ORES,  SLAGS,   MATTE,  AND  FLUE  DUST  79 

Lake  Superior  copper  deposits  contain  but  a  trace  of  sulphur, 
excepting  in  a  few  small  cross- veins.  The  Western  methods,  to 
be  described,  are  the  same  as ,  those  used  in  the  eastern  States 
and  Europe  for  all  furnace  produces. 

13.  Sulphur  in   Roasted   Ores.  —  Treat  .5   gram,  or  f   the 
sulphur  weight  (.687  gram),  with  10  c.c.  of  a  mixture  of  nitric 
acid  and  potassium  chlorate.     Evaporate  to  dry  ness  on  a  steam 
bath.     Take  up  with  5  c.c.  of  hydrochloric  acid  and  15  c.c.  of 
water.     Boil  for  a  few  minutes  and  filter  off  the  insoluble  mat- 
ter.   Bring  the  filtrate  to  a  boil,  add  barium   chloride   solution, 
BaCl2.2H2O,  using  an  amount  equivalent  to  1  gram  of  the  crystals 
for  calcines  and  2  grams  for  ores.     Allow  the  barium  sulphate 
to  settle,  filter,  and  wash  6  to  10  times  with  boiling  water.     Dry, 
ignite  at  a  dull  red  heat,   and  weigh  the  cooled  crucible  and 
barium    sulphate.     Barium     sulphate    (BaSO^  x  0.13735  =  sul- 
phur (S). 

If  accurate  work  is  required,  the  solution  must  be  repeatedly 
evaporated  with  excess  of  pure  hydrochloric  acid  in  order  that 
the  solution  may  be  free  from  all  nitrates  and  chloric  acid  before 
the  sulphuric  acid  is  precipitated. 

To  avoid  errors  which  are  introduced  by  direct  precipitation 
in  presence  of  iron,  proceed  as  follows:  After  repeated  evapora- 
tions with  hydrochloric  acid,  dissolve  in  the  dilute  acid  and 
filter.  Heat  the  filtrate  nearly  to  boiling,  make  ammoniacal, 
and  then  add  an  excess  of  barium  chloride.  Now  make  the 
liquid  slightly  acid  with  dilute  hydrochloric  acid,  allow  to  settle 
in  a  moderately  warm  place,  but  do  not  boil.  Filter,  wash  very 
thoroughly,  dry,  and  ignite.  Good  results  in  presence  of  iron 
may  also  be  obtained  by  adding  the  barium  salt  in  a  cold  solu- 
tion and  allowing  to  stand,  cold,  for  12  hours  before  filtra- 
tion. Compare  with  the  semi-electrolytic  method,  20. 

14.  Sulphide  Ores  and  Matte.  —  Add  10  to  15  c.c.  of  nitric 
acid  (d.,  1.36)  to  a  .5  gram  sample.     Place  on  the  front  of  the 
hot   plate   and   add   small   quantities   of  potassium   chlorate  at 
frequent  intervals.     When  the  sulphur  is  all  in  solution,  remove 
the  watch  glass  and  evaporate  to  dryness.     Then  proceed  as  in 
the  previous  method. 

The  solution  of  sulphur  in  some  mattes  is  difficult  and 
requires  prolonged  treatment  with  nitric  acid  and  potassium 
chlorate.  The  following  scheme  may  hasten  matters  in  such 


80  ANALYSIS  OF  COPPER 

cases:  Sprinkle  1  gram  of  potassium  chlorate  on  .5  gram  of 
sample,  add  10  to  15  c.c.  of  water,  and  bring  to  a  boil.  Add 
10  to  15  c.c.  of  nitric-chlorate  mixture  and  heat  to  boiling, 
keeping  the  solution  well  covered  until  all  the  sulphur  is  dis- 
solved. Remove  the  watch  glass,  evaporate  to  dryness  on  the 
steam  bath,  and  proceed  as  before. 

One  gram  of  barium  chloride  crystals  will  precipitate  23.4  per 
cent  of  sulphur  on  a  half-gram  sample,  and  may  be  added  in 
solution.  The  purest  barium  sulphate  is  obtained  by  having  the 
solution  of  sulphates  very  dilute,  with  only  a  few  c.c.  of  hydro- 
chloric acid  in  excess,  and  by  adding  the  barium  chloride  drop  by 
drop,  while  stirring. 

15.  With  Sulphates.  —  For  the  determination  of  total  sulphur 
in  ores  containing  barium  sulphate  or  large  quantities  of  calcium 
sulphate,  one  may  employ  a  fusion  method  (sodium  carbonate 
and    potassium    nitrate)    with    sodium    chloride.1 

16.  Sulphur  in  Lead  Ores.  —  Proceed  as  before,  after  evap- 
oration to  dryness.     Take  up  the  residue  with  5  c.c.  of  hydro- 
chloric acid  and  5  grams  of  ammonium  chloride  and  15  c.c.  of 
boiling   water.     These   reagents,    on   boiling,    will    dissolve    any 
lead  sulphate  which  may  have  formed  during  evaporation. 

17.  Sulphur   in   Ores   Carrying   Zinc.  —  Beckman's   method 
consists  in  fusing  .5  gram  of  ore  with  25  grams  of  a  (6:1)  mix- 
ture of  sodium  carbonate  and  potassium  chlorate.    The  sintering 
process  of  Waring  for  heavy  zinc  ores  is  of  a  similar  nature. 

18.  The  Sintering  Process  of  F.  G.  Hawley  is  more  simple 
than  that  of  Waring.     For  decomposition,  mix  .5  gram  of  ore 
thoroughly  with  six  to  eight  times  its  weight  of  a  mixture  of 
zinc  oxide  and   sodium    carbonate   (4:1);    sinter  at  a  low  red 
heat  for  15  minutes  in  a  porcelain   crucible,  leach  with  warm 
water,  and  filter. 

Acidulate  the  filtrate  with  hydrochloric  acid,  add  5  c.c.  in 
excess,  and  add  by  degrees  to  the  boiling  solution  a  sufficiency 
(about  20  c.c.)  of  a  semi-saturated  solution  of  barium  chloride. 
Slags  may  be  similarly  treated. 

19.  Sulphur  hi  Heavy  Pyrites.  —  The  next  two  modifications 
are  two  new  devices  of  New  York  chemists  for  the  solution  of 
rich  copper-bearing  pyrites  and  for  the  elimination  of  the  injuri- 
ous effect  of  ferric  chloride.     (Compare  method  13.) 

1  Fresenius,  Quantitative  Analysis. 


ORES,   SLAGS,   MATTE,  AND  FLUE  DUST  81 

Allen  and  Bishop 1  recommend  solution  in  a  mixture  of 
bromine  and  carbon  tetrachloride,  and  reduction  by  powdered 
aluminum  as  follows: 

1.3735  grams  of  ore  are  placed^in  a  dry  300  c.c.  Jena  beaker, 
10  c.c.  of  a  mixture  of  2  parts  of  liquid  bromine  and  3  parts  of 
carbon  tetrachloride  by  volume  are  added,  and  the  covered 
beaker  shaken  gently  for  15  minutes  at  room  temperature. 
Then  15  c.c.  of  nitric  acid  (1:4)  are  added  and  the  mixture 
allowed  to  stand  15  minutes  longer,  after  which  the  beaker  is 
heated  up  gradually  on  the  steam  bath  and  the  solution  taken 
to  dryness.  Ten  c.c.  of  hydrochloric  are  next  added,  the  solution 
evaporated  again,  and  the  silica  thereby  dehydrated.  Filter  and 
reduce  the  ferric  chloride  by  gradual  addition  of  powdered 
aluminum,  free  from  sulphur.  Precipitate  the  barium  sulphate 
in  the  cold  by  adding  a  5  per  cent  solution  of  barium  chloride 
at  the  rate  of  5  c.c.  per  minute,  the  total  volume  of  the  solution 
being  1600  c.c. 

20.  Semi-electrolytic  Method  for  Sulphur.  —  The  next 
method  quoted  is  more  accurate  than  19,  because  the  volume  of 
the  solution  is  kept  very  small,  thus  favoring  higher  results,  and 
the  interfering  metals  are  nearly  all  eliminated  from  the  solution.2 

The  ore  should  be  ground  just  to  pass  a  sieve  of  80  meshes  to 
the  linear  inch.  .5  gram  of  dried  ore  (or  .687  gram  =  J  factor 
weight)  is  placed  in  a  250  c.c.  beaker  with  a  mixture  of  3  parts 
nitric  acid  (d.,  1.42)  and  1  part  of  hydrochloric  acid  to  which  4  or 
5  drops  of  bromine  have  been  added.  Cover  the  beaker  tightly, 
and  allow  it  to  stand  at  room  temperature  for  one  half-hour. 
Transfer  to  a  steam  bath,  heat  gently  until  action  ceases,  then 
raise  the  cover,  and  evaporate  to  dryness.  Add  5  c.c.  of  hydro- 
chloric acid  to  the  residue,  heat  until  action  ceases,  wash  the 
cover,  and  evaporate  to  dryness.  Treat  with  hot  water  until 
residue  is  disintegrated,  and  wash  the  solution  into  an  electro- 
lytic beaker,  containing  a  mercury  cathode  with  insulated  wire 
connection.  Dilute  to  75  c.c.,  pass  a  current  through  a  platinum 
spiral  anode  to  the  mercury  for  5  to  6  hours  at  .8  to  1  ampere, 
or  at  a  lower  rate  overnight.  All  metals  pass  into  the  mercury. 

Siphon,  or  pour  off,  the  colorless  liquid,  wash  by  decantation 
four  times  with  25  c.c.  of  water,  then  pour  off  mercury  into 

1  Eighth  Inter.  Congress  of  Appl.  Chem.  1,  38. 

2  A.  M.  Smoot,  Eng.  and  Min.  Jour.  94,  412;  J.  Am.  Chem.  Soc.,  25,  911. 


82  ANALYSIS  OF  COPPER 

small  beaker,  and  wash  the  beaker  once  (especially  the  lip)  with 
water.  Filter  into  an  800  c.c.  beaker  and  wash  4  to  5  times  with 
hot  water.  Dilute  to  450  to  600  c.c.,  heat  to  boiling,  and  add 
to  boiling  liquid  25  c.c.  (or  34  c.c.  for  .687  gram  ore)  of  a  10 
per  cent  solution  of  barium  chloride  in  a  thin  stream.  The 
barium  sulphate  contains  impurity  amounting  to  .06  per  cent  to 
.09  per  cent  on  .5  gram  of  pyrites,  but  the  correction  for  solu- 
bility nearly  balances  this,  leaving  a  final  plus  error  of  .01  to 
.04  per  cent  of  sulphur,  as  calculated. 

The  objection  to  this  method  for  a  large  amount  of  work  is 
the  necessity  for  electrolysis  and  the  treatment  and  purification 
of  all  the  mercury.  It  seems  well  adapted  to  umpire  assaying. 
Compare  method  13. 


CHAPTER  VI 

SPECIAL  ELEMENTS  IN  ORES,   SLAGS,   AND   MATTE 
ARSENIC 

1.  Distillation  (Method  of  Skinner  &  Hawley).  —  A  distilling 
solution  is  required,  (a)  Dissolve  300  grams  pure  cupric  chloride 
crystals  in  one  liter  hydrochloric  acid  (d.,  1.20)  (solution  17, 
Chapter  III),  (b)  Dissolve  one  pound  (453.6  grams)  zinc  (free 
from  arsenic)  by  adding  to  it  gradually  a  mixture  of  1250  c.c. 
hydrochloric  acid  (1.20)  and  500  c.c.  of  water.  When  the  zinc 
has  dissolved,  evaporate  the  solution  to  1100  c.c.  (solution  58, 
Chapter  III).  Mix  (a)  and  (6).  The  principle  on  which  the 
assay  depends  is  the  evolution  of  arsenious  chloride  directly  from 
the  sulphide  by  distillation  in  a  saturated  solution  of  chlorides 
of  copper  and  zinc. 

Analysis.  —  Add  5  c.c.  nitric  acid  to  a  half-gram  sample  in  a 
small  beaker.  (A  little  potassium  chlorate  is  added  with  flue 
dust  samples.  If  desired,  Low's  method  of  decomposition  may 
be  used  as  described  in  method  7.)  When  the  action  becomes 
quiet,  add  6  to  10  c.c.  hydrochloric  and  evaporate  to  complete 
dryness  on  steam  bath.  As  there  is  danger  of  loss,  the  tempera- 
ture should  be  low.  Take  up  with  5  c.c.  hydrochloric  acid  and 
25  c.c.  of  water.  Bring  to  a  boil  and  filter  off  the  insoluble  mat- 
ter. Dilute  the  filtrate  to  200  c.c.  with  boiling  water.  Add 
sufficient  sodium  sulphite  to  render  the  solution  colorless.  Boil 
off  the  excess  of  sulphur  dioxide  and  add  15  c.c.  hydrochloric 
acid.  Pass  a  current  of  hydrogen  sulphide  through  the  solution 
until  it  is  saturated.  Filter  off  the  precipitated  sulphides,  wash 
out  the  iron  salts,  and  place  the  sulphides  in  a  flask  connected 
to  an  8-inch  (20  cm.)  Allihn  condenser,  with  large  straight  bulb 
tube,  set  vertically.  Never  allow  the  lower  end  of  condenser  to 
be  more  than  sealed  by  the  water  in  beaker  (200  c.c.).  Add 
50  c.c.  of  " distilling  solution"  and  distil  carefully  until  the 
thermometer  reads  115°  C.  Remove  the  flask  from  the  heat  and 


84  ANALYSIS  OF  COPPER 

add  25  c.c.  of  hydrochloric  acid.  Distil  again  until  the  ther- 
mometer reads  115°  C.  Pour  distillate  into  a  No.  3  beaker, 
make  alkaline  with  ammonia  (about  25  c.c.  being  required), 
just  acidify  with  dilute  hydrochloric  acid.  Cool,  add  2  to  4 
grams  of  bicarbonate  of  soda  and  a  little  starch  solution,  and 
titrate  with  standard  iodine  solution.  (Use  20,  Chapter  III.) 
On  samples  low  in  arsenic,  1  to  5  grams  of  sample  may  be  taken. 
Rapid  and  complete  precipitation  of  arsenic,  in  samples 
containing  only  small  quantities  of  other  hydrogen  sulphide 
metals  may  be  affected  by  adding  100  mg.  of  pure  copper  to  the 
sample.  Antimony  and  tin  may  be  estimated  in  the  residue 
from  distillation. 

2.  In  Slags  (Skinner  &  Hawley).  —  Treat  5  to  10  grams  with 
10  c.c.  nitric  acid,  10  c.c.  hydrofluoric,  and  2  c.c.  sulphuric  acid. 
Evaporate  to  sulphuric  fumes.     Take  up  with   10  c.c.   hydro- 
chloric acid  and  25  c.c.  water,  then  boil  and  filter.     Dilute  fil- 
trate to   500   c.c.     Almost  neutralize   with   ammonia.     Reduce 
with  sodium  sulphite  and  proceed  as  before.     Hydrofluoric  acid 
is  not  necessary  in  the  case  of  chilled  slags. 

3.  Sintering  Method  (F.  G.  Hawley).  —  Mix  .5  to  1  gram  of 
ore  with  six  to  ten  parts  of  an  equal  mixture  of  zinc  oxide  and 
sodium   carbonate.     Sinter  in   a  porcelain  crucible  for  15  to  20 
minutes.     Start  at  a  low  red  heat  and  increase  to  full  redness. 
Leach  with  hot  water  and  filter.     Boil  solution  carefully,  neutral- 
ize with  nitric  acid,  and  add  just  4  drops  excess,  using  litmus 
paper  as  an  indicator.     See  that  any  alumina  or  zinc  oxide,  that 
may  have   run  through   the  filter,  is  dissolved.     Boil  the  solu- 
tion to  remove  carbonic  acid  gas,  remove  from  the  hot  plate, 
and    add    a  solution    of    silver    nitrate.    Seven-tenths    gram    of 
silver  nitrate  is  sufficient  for  .1  gram  of  arsenic.     No  red  pre- 
cipitate should   be    visible.      If    any    appears,  add  a  few  drops 
of    nitric    acid   until   dissolved.      Now    add    about    1    gram    of 
sodium  acetate,  and   stir  rapidly.    Let   stand  for    20    minutes, 
filter,    and   wash.      Dissolve    the    silver    arsenate    through    the 
filter  with    dilute    nitric    acid,    dilute    the    solution,  and    titrate 
with  a  standard  solution  of  ammonium  thiocyanate,  using  ferric 
sulphate  as  an  indicator.     (Solution  8,  Chapter  III.) 

4.  Evolution  as  Arsine  l   (Modification  of  Cobeldick) .  —  For 

1  F.  W.  Schmidt,  J.  Anal  and  Appl  Chem.  (1892),  408;    Heath,  Eng. 
and  Min.  Jour.  63,  663. 


ELEMENTS  IN  ORES,   SLAGS,  AND  MATTE  85 

determination  of  traces  of  arsenic,  2  grams  of  ore  are  weighed 
into  a  150  c.c.  beaker,  10  c.c.  of  strong  nitric  acid  added,  covered 
with  a  watch  glass,  and  allowed  tg  digest  all  night  in  a  warm 
place.  The  liquid  is  diluted  to  100  c.c.  and  excess  ammonia 
added,  boiled,  cooled,  filtered,  and  washed  in  cold  water.  The 
hydroxides  are  dissolved  in  dilute  sulphuric  acid  (1:10),  evapo- 
rated dry,  and  fumed  on  a  silica  plate.  The  mass  is  taken  up 
with  water,  and  a  little  sulphuric  acid  if  necessary,  the  bulk  of 
solution  being  about  50  c.c.,  warmed  to  dissolve  all  soluble  mat- 
ter and  transferred  to  a  Marsh  apparatus  which  is  generating 
hydrogen  from  pure  zinc  and  sulphuric  acid  or  hydrochloric  acid. 
(A  better  reduction  is  secured  by  adding,  also,  .5  c.c.  of  80 
per  cent  solution  of  stannous  chloride.)  The  arsenic  mirror  is 
concentrated  in  the  constricted  portion  of  the  tube  and  is  com- 
pared with  standard  mirrors  made  with  known  amounts  of 
arsenic  brought  into  the  solution  (in  presence  of  a  trace  of  iron 
salt).  If  the  material  contains  more  than  .1  per  cent  of  arsenic, 
the  portion  of  the  tube  containing  the  mirror  is  cut  off,  weighed, 
the  tube  cleaned,  and  re  weighed.  (Ericsson  proposes  to  con- 
duct the  gas  through  .1  normal  silver  nitrate,  add  excess  hydro- 
chloric, filter,  neutralize,  and  titrate  with  .002  normal  iodine 
solution.)  Antimony  reacts  also,  if  present.1 

Gutzeit  Test.  —  Allen  &  Palmer  have  recently  presented  a 
modified  Gutzeit  test  which  may  be  useful  for  continuous  work  in 
the  estimation  of  traces  of  arsenic.2 

5.  Nitrate   Fusion.3  —  Fuse  1    to  5  grams   of   the   ore  with 
six  to  'ten  times  its   weight  of  an  equal  mixture  of  sodium  and 
potassium  nitrates,  and  precipitate  the  arsenic  from  the  aqueous 
solution   with   silver   nitrate.     The   crucible   is,    however,    con- 
siderably attacked. 

6.  Semi-fusion  with  Potassium  Bisulphate.  —  The  following 
method  of  A.  H.  Low 4  is  remarkably  accurate  for  ores  which 
can  be  thus  decomposed.     The  first,  or  distillation,  method  is 
so  much  quicker  that  it  seems  to  be  preferred  in  the  largest 
works,  although  it  may  be  combined  with  the  method  of  solu- 
tion described  in  the  next  paragraph. 

1  Svensk  Farm.  Tidskrift,  18,  473  (1914). 

2  Eighth  Inter.  Congress  Appl.  Chem.  1,  9. 

3  Method  of  Dr.  R.  Pearce. 

4  J.  Am.  Chem.  Soc.  28,  1715. 


86  ANALYSIS  OF  COPPER 

Digest  .5  gram  of  ore  with  7  grams  potassium  bisulphate, 
.5  gram  tartaric  acid,  and  10  c.c.  strong  sulphuric  acid,  to  a 
clear  melt,  sulphur-free.  After  cooling,  the  melt  is  dissolved  in 
60  c,c.  of  (1:  5)  hydrochloric  acid  with  2  to  3  grams  tartaric  acid, 
diluted  and  treated  with  hydrogen  sulphide.  Sulphides  are 
dissolved  in  potassium  sulphide  and  filtered  into  a  300  c.c.  flask. 
Three  grams  bisulphate  and  5  c.c.  sulphuric  are  added,  the 
mixture  boiled  down  again,  cooled,  and  taken  up  with  75  c.c. 
of  (2:1)  hydrochloric  acid  and  hydrogen  sulphide  passed  again. 
Moisten  the  filter  with  acid  of  the  same  strength,  and  wash  with 
the  mixture.  The  arsenic  is  now  on  the  filter,  and  antimony 
and  tin  should  be  in  the  filtrate.  From  this  point  the  three 
are  treated  separately.  First,  the  arsenic  is  determined  by  dis- 
solving the  sulphide  in  a  little  ammonium  sulphide,  washing  into 
a  300-c.c.  Jena  flask,  and  reducing  with  complete  expulsion  of 
sulphur  by  boiling  vigorously  with  2.5  grams  of  potassium  bi- 
sulphate and  5  to  10  c.c.  of  sulphuric  acid  (d.,  1.84).  Titrate 
the  cold  aqueous  solution  of  the  paste  by  iodine  as  directed  for 
"arsenic  in  copper,"  Chapter  XII.  Use  iodine  solution  20, 
Chapter  III. 

It  is  necessary  to  boil  the  solution  in  the  Jena  flask  very 
hard,  after  the  water  is  expelled,  in  order  that  the  acid  fumes 
may  carry  all  sulphur  out  of  the  neck  of  the  flask.  The  solu- 
tion should  be  titrated  within  a  few  hours  after  reduction.  One 
cubic  centimeter  of  iodine  =  .005  gram  arsenic. 

ANTIMONY 

7.  Antimony  in  Ores  is  finally  estimated,  according  to  Low, 
by  diluting  the  filtrate  from  arsenic  (6)  with  four  parts  of  water, 
separating  the  antimony  as  sulphide  by  treatment  with  hydrogen 
sulphide,  and  reducing  by  digestion  in  a  Jena  flask,  in  the  same 
way  as  for  arsenious  sulphide,  but  with  double  the  quantity  of 
potassium  bisulphate  and  sulphuric  acid.     Expel  all  the  sulphur 
and  most  of  the  free  acid,  cool,  add  50  c.c.  of  water  and  10  c.c. 
of  hydrochloric  acid.     Dilute  to  200  c.c.  with  cold  water  and 
titrate  with  standard   potassium   permanganate.     Multiply  the 
iron  value  by  1.0751,  or  the  oxalic  acid  value  by  .9532  to  obtain 
the  titer  for  antimony. 

8.  Antimony  may  also  be  estimated  by  dissolving  the  ores, 
or  slags,  etc.,  in  a  mixture  of   acids,  filtering  and  fusing  any 


ELEMENTS  IN  ORES,   SLAGS,  AND  MATTE  87 

residue  with  carbonates  and  nitrate  of  sodium,  then  separating 
the  arsenic  and  antimony  frojn"  the  precipitated  sulphides  by 
treatment  with  dilute  sodium  sulphide  solution.  Evaporate  the 
alkaline  solution  to  dry  ness  on  the  water-bath  or  steam  plate. 
Then  oxidize  the  sulphur  by  digestion  with  red,  fuming  nitric 
acid,  evaporate  to  dryness  again,  and  dissolve  the  salts  in  25 
c.c.  of  water,  or  more.  Add  an  amount  of  hydrochloric  acid 
(d.,  1.2),  equal  to  twice  the  volume  of  the  solution  of  the  arsenic 
group,  and  precipitate  the  arsenic  alone  by  hydrogen  sulphide. 
Filter,  testing  the  filtrate  again.  Wash  with  acid  of  the  same 
strength.  Then  dilute  the  filtrate  with  4  parts  of  water  and 
precipitate  the  antimony,  and  tin  if  present,  observing  the  pre- 
cautions of  method  3,  Chapter  XII.  Antimony  may  likewise 
be  dissolved  out  of  the  mixed  sulphides  as  in  10.  Tin  may  also 
be  separated  from  antimony  according  to  method  11,  the 
arsenic  having  been  previously  removed  as  just  described. 

9.  Antimony  by  Electrolysis.  —  Simple  ores  are  decomposed 
by  digestion  with  acids  or  by  Low's  process.  Refractory  ores 
may  be  decomposed,  after  Hawley's  formula,  by  mixing  1  to  2 
grams  of  ore  with  8  to  10  parts  of  a  (1:1)  mixture  of  sodium 
carbonate  and  flowers  of  sulphur  and  heating  slowly  in  a  covered 
porcelain  crucible  for  15  minutes,  finishing  at  a  moderate  red 
heat.  Cool  with  the  cover  on,  leach  with  hot  water,  and  boil 
for  five  minutes.  If  the  precipitate  does  not  settle  readily,  or 
the  solution  appears  green,  add  2  to  4  grams  of  sodium  sulphite, 
and  boil  again.  Make  up  to  200  c.c.  and  pass  through  a  dry  filter 
into  a  dry  beaker.  Remove  100  c.c.  to  a  300  c.c.  beaker,  acidify 
with  acetic  acid,  using  10  c.c.  in  excess,  and  boil  for  one  minute. 

For  accurate  work,  the  filtered  sulphides  should  be  dissolved 
in  ammonium  sulphide  (or  sodium  and  potassium  sulphides  in 
presence  of  copper),  and  precipitated  a  second  time  with  acetic 
acid. 

The  antimony  may  be  dissolved  out  by  boiling  (1  : 1)  hydro- 
chloric acid  and  titrated,  ignited  with  nitric  acid  in  a  porcelain 
crucible  and  weighed,  according  to  Fresenius,  as  tetroxide,  —  or 
the  compound  may  be  electrolyzed,  —  if  the  antimony  is  present 
in  quantity. 

Electrolysis.  —  Dissolve  the  sulphides  in  15  c.c.  of  sodium 
monosulphide  (solution  52).  W.  B.  Price  recommends  a  solu- 
tion of  1.18  specific  gravity,  or  density.  Dilute  to  70  c.c.,  add 


88  ANALYSIS  OF  COPPER 

3  grams  of  potassium  cyanide,  and  electrolyze  in  a  Frary  rotary 
apparatus  (or  solenoid),  with  a  current  of  6  amperes  and  an 
electrode  tension  of  4  volts. 

TIN   (WITH  ARSENIC  OR  ANTIMONY) 

10.  If  Tin  is  present  in  quantity,  evaporate  the  filtrate  from 
arsenic   to    dryness    on   the    steam    plate    after    adding   enough 
potassium  chloride  to  form  a  double  salt  with  the  tin  and  anti- 
mony.    Redissolve  by  boiling  for  one  hour,  if  necessary,  with  a 
mixture  of  5  grams  of  ammonium  oxalate  and  5  grams  of  oxalic 
acid  dissolved  in  100  c.c.  of  water  (a  solution  proposed  by  G.  W. 
Thompson) . 

Precipitate  the  antimony  from  the  hot  liquid  by  gaseous 
hydrogen  sulphide  and  filter  the  hot  solution.  Dissolve  the 
sulphide  in  a  very  little  hot  dilute  sodium  sulphide,  pour  into  a 
boiling  solution  of  half  the  former  quantity  of  the  oxalic  mix- 
ture, and  repeat  the  precipitation  and  filtration.  Boil  out  the 
hydrogen  sulphide,  and  electrolyze  the  combined  filtrates  for 
tin.  The  solution  should  be  kept  in  circulation  by  a  slow  stream 
of  air,  or  by  a  revolving  anode. 

Time  2.5  hours,  and  current  .8  ampere  per  sq.  decimeter.  This 
procedure  gives  a  much  better  separation  of  tin  and  antimony 
than  is  possible  with  the  original  method  of  Clarke.  Refer  to  the 
special  volumetric  method,  12,  Chapter  VII  and  to  "  Antimony," 

Chapter  XII. 

BISMUTH 

11.  Combination  Assay.  —  An  approximate  test  of  ores  and 
slags  may  be  made  by  fire  assay  as  for  lead,  adding  enough  pure 
lead  to  obtain  an  average  button.    This  button  is  then  flattened, 
dissolved  in  dilute  nitric  acid,  the  solution  made  up  to  a  definite 
volume  with  dilute  sulphuric  acid,  shaken,  and  a  known  portion 
quickly  filtered  through  a  dry  filter  into  a  calibrated  flask,  and  sub- 
sequently evaporated  to  fumes  of  sulphur  trioxide.     The  "den- 
sity" of  the  lead  sulphate  is  taken  as  4-f  nearly,  or  the  volume 
of  the   sulphate   from   75   grams   of  lead  =  16.875   c.c.    (L.   G. 
Eakins) . 

The  volume  of  the  lead  precipitate  is  deducted  from  the  total 
volume.  After  the  residue  from  evaporation  has  been  taken  up 
with  water,  any  lead  sulphate  is  filtered  out,  hydrogen  sulphide 
is  passed  in  for  10  to  15  minutes,  the  sulphides  filtered  off,  and 


ELEMENTS  IN  -ORES,  SLAGS,  AND  MATTE  89 

extracted  with  yellow  potassium  sulphide.  Dissolve  the  insolu- 
ble sulphides  in  fuming  nitric  acid,  and  evaporate  again  with  3 
to  5  c.c.  of  sulphuric  acid.  Filter  and  wash  again,  make  the 
liquid  slightly  alkaline  with  sodium  carbonate,  and  add  a  few 
drops  of  potassium  cyanide.  Boil,  allow  to  settle,  filter  on  a  fine 
paper,  wash  with  warm  water,  and  redissolve  in  a  little  nitric 
acid.  Finally,  separate  the  bismuth  by  precipitation  with  an 
excess  of  ammonia  and  ammonium  carbonate,  ignite  very  care- 
fully in  a  porcelain  crucible  at  a  low  red  heat,  avoiding  undue 
reducing  conditions,  and  weigh  as  bismuth  sesquioxide,  Bi203. 

12.  Bismuth  (Accurate  Analysis).  —  Decompose  the  ore  with 
nitric  acid  and  evaporate  nearly  to  dry  ness.     The  sample  of  .5 
to  1  gram  is  then  treated  with  about  5  c.c.  of  hydrochloric  acid 
and  heated  until  the  solution  clears.     Then  add  10  to  15  c.c.  of 
sulphuric  acid,  and  evaporate  to  fumes  of  sulphur  trioxide.    Fil- 
ter out  the  lead  sulphate,  treat  the  solution  with  hydrogen  sul- 
phide gas  to  saturation,  filter  and  extract  the  mixed  sulphides 
with  yellow  potassium  sulphide,  or  ammonium  sulphide.     Bis- 
muth is  rather  soluble  in  sodium  sulphide,   alone.     As  copper 
sulphide  is  generally  present,  wash  the  mass  back  into  the  beaker, 
and  warm  for  some  time  with  3  to  4  grams  of  potassium  cyanide. 
Cadmium  sulphide  and  a  trace  of  lead  will  remain  with  the  bis- 
muth.    Dissolve  in  nitric  acid  (1  :  2),  filter,  wash  well,  dilute  to 
250   to   300   c.c.,    neutralize   the   boiling   liquid   with   ammonia 
(1  : 2),   until  the  last  drops  make  the  solution  faintly  cloudy. 
Then  add  1  c.c.  of  dilute  hydrochloric  acid  (1  : 3),  and  keep  hot 
for  about  an  hour.     Filter  on  a  weighed  filter,  or  asbestos  felt, 
dry  at   100°  C.,   and  weigh  as  the  basic  chloride,  BiOCl,   con- 
taining 80.17  per  cent  of  bismuth.     The  basic  salt  may  be  also 
redissolved,   if   preferred,    then   precipitated   as   carbonate,    and 
finally  ignited  to  oxide. 

BARIUM 

13.  Barium,  as  obtained  in  the  "  determination  of  insoluble 
residue,"  or  silica,  and  ferrous  oxide  (Chapter  V),  remains  in- 
soluble after  the  silica  is  driven  off  with  excess  of  hydrofluoric 
and  sulphuric  acids.    When  an  insoluble  residue  is  obtained  from 
a  leady  ore,  the  first  insoluble  residues  should  be  boiled  with 
water  containing  5  grams  of  ammonium  chloride.    Then  fuse  the 
weighed  residue  as  described  in  the  method  for  "  insoluble  matter 


90  ANALYSIS  OF  COPPER 

in  barium  sulphate  ores"  (1,  Chapter  V),  and  obtain  the  barium 
in  the  form  of  pure  sulphate  for  weighing. 


CADMIUM 

14.  Cadmium  is  a  rare  constituent  of  regular  copper  ores, 
and  its  determination  would  only  be  required  in  heavy  zincy 
ores.    One  gram  of  such  material  may  be  decomposed  with  acids 
until  the  metals  are  dissolved.     Evaporate  the  liquid  with  10 
c.c.  of  (1  : 1)  sulphuric  acid,  until  strong  fumes  of  sulphur  triox- 
ide  are  evolved.     Cool,  dilute  to  50  c.c.,  filter  off  the  lead  sul- 
phate, if  much  is  present  and  wash  with  a  very    little    dilute 
sulphuric  acid   (1  : 20).      Filtration   is   not,    however,    necessary 
at  this  stage,  if  the  heavy  metals  are  to  be  removed  from  the 
solution  by  reduction  with  aluminum.     Such  a  reduction  may 
carry  down  a  part  of  the  cadmium,  which  must  be  recovered 
by  dissolving  the  precipitated  metals  and  repeating  the  reduc- 
tion.    To  separate  the  iron,  zinc,  and  cadmium,  proceed  accord- 
ing to  "BreyerV  method  for  zinc."     (18  a,  Chapter  VII.)     The 
heavy    metals    may    also    be    precipitated    as    sulphides    from 
hot    (1:5)  sulphuric   acid,  or  the  copper  may  be  removed   as 
thiocyanate  (3,  Chapter  IV). 

If  preferred,  the  purified  cadmium  sulphide  may  finally  be 
dissolved  and  titrated  like  zinc,  standardizing  the  potassium 
ferrocyanide  with  pure  cadmium.  The  cadmium  may  also  be 
precipitated  as  phosphate  according  to  the  conditions  prescribed 
in  21,  Chapter  XIV  for  "zinc  in  standard  brass."  Factor: 
Cd2P207  X  .56358=  weight  of  cadmium. 

15.  Chromium  in  chromite  or  furnace  refractories  may  be 
accurately    estimated    by    the     volumetric    method    of    A.    G. 
McKenna.1     It  is  necessary  to  grind  the  material  in  an  agate 
mortar  (after  coarse  crushing)  to  pass  a  sieve  of  100  meshes  to 
the  linear  inch  (or  40  per  cm). 

Fuse  .5  gram  of  the  powder  with  sodium  peroxide  in  a 
nickel  crucible  for  one  minute,  or  until  decomposed.  The  mass 
is  extracted  with  water,  filtered  into  a  500  c.c.  flask  and  the 
filtrate  boiled  ten  minutes  to  destroy  the  peroxide.  Acidify 
the  cool  solution  with  a  large  excess  of  dilute  (l  :4)  sulphuric 
acid,  transfer  to  a  liter  beaker  and  dilute  to  800  c.c.  with  cold 

1  Proc.  Eng.  Soc.  W.  Pa.,  16,  119  —  Methods  of  Iron  Analysis,  Phillips,  156. 


ELEMENTS  IN  ORES,   SLAGS,  AND  MATTE  91 

water.  To  this  solution  add  100  c.c.  of  ammonium  ferrous 
sulphate  solution  (equivalent  ^tcr  7  grams  of  metallic  iron  per 
liter).  This  will  reduce  chroma^e  equivalent  to  .3176  gram  of 
chromium  sesquioxide.  '"  The  excess  of  ferrous  sulphate  may 
then  be  titrated  with  potassium  permanganate  (3.692  grams  per 
liter),  although  solution  41  and  42  of  Chapter  III  may  be  used 
equally  well.  For  continuous  work  the  two  are  made  of  equal 
value  in  chromium  —  3  Fe=Cr,  or  167.52  grams  Fe  reduce  52.0 
grams  Cr. 

The  iron  in  the  insoluble  residue  may  be  determined  by 
titration,  as  in  the  analysis  of  refractories,  23,  Chapter  VII. 

For  the  complete  analysis  of  chrome  ores  refer  also  to  method 
23  of  the  next  chapter. 

16.  Cobalt  is  included  with  nickel,  methods  1-3,  Chapter  VII, 
in  order  to  avoid  duplication. 

FLUORINE 

17.  Fluorine  is  known  to  exist  in  ores  chiefly  in  the  form  of 
calcium  fluoride,  and  some  metallurgists  contend  that  it  is  of  no 
value  as  an  active  base.     Accordingly  a  reliable  method  for  its 
estimation  is  included.     It  can  be  roughly  determined  by  the 
process  recommended  by  A.  H.  Low  for  such  material.     In  car- 
bonates (fluxes),  this  is  a  simple  problem.     The  carbonates  are 
boiled  in  strong  acetic  acid,  after  fine  grinding.     Then  add  some 
dilute  acid  and  the  calcium  fluoride  with  silicates  will  remain 
insoluble.    For  an  accurate  estimation,  however,  proceed  accord- 
ing to  Kneeland's  method  in  the  following  paragraphs.1 

Fuse  .5  to  1  gram  of  ore,  or  slag  (according  to  the  percentage 
of  fluorine),  in  a  porcelain  crucible,  with  10  times  its  weight  of 
a  mixture  of  equal  parts  of  sodium  and  potassium  carbonates. 
When  the  whole  mass  has  come  to  a  quiet  fusion,  raise  the  heat 
to  a  bright  red,  and  pour  into  an  iron  mold,  saving  the  crucible. 
Cool,  break  up  the  crucible  into  small  pieces,  and  transfer 
with  the  fused  mass  to  a  15  cm.  casserole  (agate  ware  preferred 
to  avoid  bumping).  Add  200  c.c.  of  water,  and  digest  for  one 
hour  at  a  temperature  near  boiling,  breaking  up  the  fused  lumps 
with  a  thick  glass  rod.  If  any  lumps  are  still  noticed,  remove 
them  with  pincers,  grind  them  in  an  agate  mortar,  and  wash  the 

1  Modification  of  Berzelius'  Method  —  Berichte  21  (1888)  2843.  Notes  — 
/.  Amer.  Chem.  Soc.  37  (1915)  258. 


92  ANALYSIS  OF  COPPER 

mass  back  into  the  casserole  with  hot  water.  Now  boil  for  10 
minutes,  and  filter  through  a  loose  paper  into  a  liter  beaker. 
Wash  first  with  hot  water,  then  with  a  hot  solution  of  ammo- 
nium carbonate,  discarding  the  residue.  Add  to  the  filtrate  10 
grams  of  ammonium  carbonate,  boil  five  minutes,  and  allow  to 
stand  in  the  cold  for  two  hpurs.  Filter  through  a  loose  filter  into 
an  agate-ware  casserole,  decanting  as  much  as  possible  of  the  fluid. 
Wash  once,  or  twice,  with  cold  water. 

To  eliminate  final  traces  of  silica,  add  20  c.c.  of  an  emulsion 
of  zinc  oxide  in  ammonium  hydroxide,  and  boil,  with  the  dish 
uncovered,  until  no  more  odor  of  ammonia  is  detected.  Filter 
into  a  750  c.c.  beaker  and  wash  with  hot  water.  To  the  filtrate, 
add  a  solution  of  calcium  chloride,  stirring  with  a  rubber-tipped 
rod  until  no  more  precipitate  is  formed.  Allow  to  settle  and 
filter,  washing  with  hot  water.  Test  the  filtrate  for  carbonates 
and  fluorine  with  a  few  drops  of  calcium  chloride  solution. 

Now  transfer  the  filter  and  precipitate  to  a  platinum  dish  of 
suitable  size.  Dry  first,  then  ignite  at  a  red  heat  for  20  minutes. 
Cool  and  disintegrate  the  mass  with  hot  water.  Add  acetic  acid 
until  the  solution  is  clear  and  evaporate  to  dryness,  being  care- 
ful not  to  decompose  the  residue.  Moisten  again  with  acetic  acid 
and  evaporate  until  there  is  no  more  odor  of  the  acid.  Wash 
the  mass  into  a  400  c.c.  beaker  with  hot  water,  add  more  water 
and  warm  until  the  calcium  acetate  is  all  dissolved,  and  add, 
finally,  150  c.c.  more  of  hot  water,  while  stirring.  Digest  for  a 
few  minutes  in  a  warm  place  and  filter,  washing  first  with  hot 
water,  then  with  hot  ammonium  chloride,  and  again  with  hot 
water. 

Next,  transfer  filter  and  contents  to  a  platinum  dish,  dry,  and 
ignite.  Cool,  moisten  with  cold  water,  add  6  c.c.  of  sulphuric 
acid  (d.,  1.84),  and  heat  for  a  few  minutes,  cool  again,  add  3  c.c. 
of  hydrochloric  acid,  and  heat  for  a  few  minutes  more.  Cool, 
dilute,  and  transfer  the  contents  to  a  250-c.c.  beaker.  Add  5 
grams  of  ammonium  chloride,  boil  for  a  few  minutes,  cool,  and 
add  an  excess  of  strong  ammonia.  Add  2  to  3  c.c.,  of  strongest 
hydrogen  peroxide,  boil,  and  filter.  The  lime  is  then  all  pre- 
cipitated from  the  filtrate  with  ammonium  oxalate  and  deter- 
mined as  calcium  oxide  in  the  usual  manner  by  titration  with 
permanganate  of  potash  (1  c.c.  =  .005  g.  CaO).  CaO  x  1.392 
gives  calcium  fluoride  (CaF2),  and  CaF2  X  0.4782  =  fluorine. 


ELEMENTS  IN  ORES,  SLAGS,  AND  MATTE  93 

In  the  analysis  of  fluor-spar,  add  4  parts  of  silica  before  the  first 
fusion. 

LEAD  — IN   ORES^AND   MATTES 

18.  Western  Assay,  —  Ores.  —  Decompose  .5  gram  in  a  cas- 
serole with  10  c.c.  of  nitric  and  10  c.c.  of  sulphuric  acid  (diluted 
with  1  part  of  water) .    Heat  until  fumes  of  sulphur  trioxide  have 
been  escaping  for  at  least  five  minutes.     It  is  extremely  impor- 
tant that  all  nitric  acid  be  expelled.     Cool,  add  50  c.c.  of  cold 
water  and  boil  until  all  soluble  sulphates  are  dissolved.     Filter, 
wash   several  times  with    hot   dilute    sulphuric   acid    (1  :  10   of 
water),  then  once  with  hot  water.    All  the  iron  must  be  removed 
from  the  precipitate.     Spread  the  filter  on  a  watch  glass  and 
wash  into  a  beaker  with  hot  water,  followed  by  hot  solution  of 
ammonium  acetate  in  sufficient  quantity  to  dissolve  all  the  lead 
sulphate.     Finally,   heat  to   boiling  and  titrate   with   standard 
ammonium  molybdate   (solution  3,   Chapter  III).     With  some 
ores,  it  may  be  necessary  to  make  a  preliminary  digestion  in 
hydrochloric  acid  before  the  nitric  and  sulphuric  acids  are  added. 

19.  Lead  in  Tailings.  —  Take  5  grams  and  proceed  as  before, 
except   that   the   solution   of  the   lead   sulphate   in   ammonium 
acetate  should  be  filtered  from  the  insoluble  matter  in  order  to 
give  a  clear  solution  for  titration.     This  scheme  will  not  give 
a  very  exact  assay  of  small  amounts  of  lead,  but  will  always  show 
the  presence  of  lead,  which  may  be  estimated  with  fair  accuracy, 
by  the  cloudiness  produced. 

The  method  above  described  is  reliable  in  presence  of  the 
elements  usually  present,  except  barium  and  strontium.  In 
this  case,  proceed  as  before  until  the  lead  sulphate  and  insolu- 
ble matter  is  on  the  filter;  then  dissolve  it  by  boiling  in  a  mix- 
ture of  50  c.c.  of  water,  .5  c.c.  of  hydrochloric  acid,  and  10  grams 
of  crystallized  ammonium  chloride.  From  the  solution,  pre- 
cipitate the  lead  with  a  strip  of  aluminum;  wash  the  deposit 
thoroughly,  dissolve  it  in  dilute  nitric  acid,  and  proceed  as  in 
the  standardization  of  the  molybdate  (solution  3),  by  lead  foil. 
(See  Chapter  III.) 

20.  Lead  by  Electrolysis.  —  The  original  description  of  F.  G. 
Hawley  1  is  modified  as  follows  :    Digest  .8643   gram  of  ore  in 
a  tall  300  c.c.  beaker  with  15  c.c.  of  chlorate  mixture  and  evapo- 

1  Eng.   &  Min.  Jour.  (1910)  648. 


94  ANALYSIS  OF  COPPER 

rate  to  fumes  of  sulphur  trioxide.  The  acid  mixture  is 
composed  of  1  part  sulphuric  acid,  2  parts  of  nitric  acid,  and 
1  part  of  a  saturated  solution  of  potassium  chlorate  in  nitric 
acid. 

Cool,  add  25  c.c.  of  water,  and  bring  to  a  boil  to  insure  per- 
fect solution  of  soluble  matter.  Now  set  the  beaker  in  an  in- 
clined position  in  a  funnel  so  that  the  lead  sulphate  may  collect 
in  one  place.  Cool  again  and  decant  with  care  through  an  S.  & 
S.  597  filter,  keeping  the  lead,  as  far  as  possible,  in  the  beaker. 
Wash  once  with  a  very  little  water,  allow  to  settle,  decant  again, 
and  wash  the  filter  once  with  a  little  cold  water.  Place  the 
beaker  under  the  funnel,  and  wash  the  filter  with  40  c.c.  of  a 
boiling  mixture  of  the  following  formula  (20  c.c.  nitric  acid,  15 
c.c.  of  saturated  ammonium  nitrate,  and  5  c.c.  of  water).  Boil 
to  ensure  complete  solution  of  the  lead,  rinse  into  a  small  90- 
c.c.  electrolytic  beaker,  and  electrolyze  the  hot  solution  for  two 
hours  with  a  current  of  1.5  to  2  amperes  (at  a  temperature  of 
about  70°  C.).  Wash  the  anode  deposit  with  hot  water,  then 
with  alcohol,  dry  over  a  hot  plate,  and  weigh.  According  to 
Hawley,  the  factor  .855  then  gives  the  percentage  of  lead  in  the 
deposit,  and  the  weight  of  lead  peroxide  gives  by  inspection  the 
percentage  of  lead.  Prof.  E.  F.  Smith  has  proved,  however,  that 
the  factor  .8643  is  more  uniformly  correct  for  the  lead  in  the 
peroxide,  provided  that  the  anode  deposit  is  dried  20  minutes, 
or  more,  in  a  hot-air  oven  at  210  to  230°  C.  The  author 
recommends  this  procedure. 

Some  operators  prefer  to  dissolve  the  lead  sulphate  with  warm 
saturated  ammonium  carbonate  and  excess  of  ammonia,  then 
mix  suddenly  with  the  proper  amount  of  nitric  acid.  Dr.  Toisten 
uses  ammonium  tartrate,  in  which  case  the  lead  may  be  pre- 
cipitated as  metal  (10,  Chapter  XIII). 

21.  Rapid  Electrolysis.  —  In  the  absence  of  antimony,  bis- 
muth, molybdenum,  or  tellurium,  the  assays,  already  described, 
may  be  shortened,  and  may  also  become  an  accurate  process  for 
the  estimation  of  traces  of  lead  which  cannot  be  accurately 
determined  as  the  sulphate.  Treat  the  factor  weight  of  ore 
(.8643  g.)  in  a  tall  90  c.c.  beaker  with  10  c.c.  of  nitric  acid. 
When  decomposed,  add  15  c.c.  of  nitric  acid,  fill  with  hot 
water,  and  electrolyze  the  nearly  boiling  solution,  as  before; 
employing  the  Frary  solenoid,  if  desired,  and  increasing  the 


ELEMENTS  IN  ORES,   SLAGS,  AND  MATTE  95 

current  to  3  or  5  amperes.  Time  of  electrolysis,  15  to  20 
minutes. 

Copper  in  solution  has  a  good  influence  on  the  deposition  of 
lead.  If  copper  or  similar  metalfc  are  absent,  it  is  necessary  to 
increase  the  volume  of  the  nitric  acid  in  the  hot  solution  to 
about  30  per  cent.  It  is  sometimes  an  advantage  to  interrupt 
the  current  for  a  minute,  during  electrolysis,  to  allow  any 
trace  of  lead  to  dissolve  from  the  cathode.  Bismuth  and  tin 
tend  to  come  down  with  the  lead,  if  appreciable  amounts  are 
present,  but  may  be  removed  after  the  deposit  is  weighed. 

22.  Chromate  Method  for  Calcareous  Ores.  —  H.  A.  Guess l 
devised  a  process  for  low-grade,  limy  material  which  is  not  readily 
tested  by  the  molybdate  method.  The  standard  solutions  are: 
potassium  chromate,  100  grams  per  liter  (solution  36,  Chapter 
III);  sodium  thiosulphate  solution  containing  either  18  or  36 
grams  per  liter.  Solution  50,  Chapter  III,  adopted  for  the 
iodide  titration  of  copper,  may  also  be  used  for  lead,  if  stand- 
ardized against  pure  lead. 

Analysis.  —  To  an  ore-charge  of  1  to  5  grams  in  a  broad 
250  c.c.  beaker,  add  3  to  5  c.c.  of  strong  nitric  acid,  15  c.c. 
of  hydrochloric  acid,  and  digest  until  all  soluble  matter  is  dis- 
solved and  the  excess  of  acid  is  reduced  to  about  8  c.c.  The 
time  required  is  15  minutes.  Remove  the  flask  and  add  a  slight 
excess  of  dilute  ammonia.  Eighty  per  cent  acetic  acid  is  then 
added  slowly  with  vigorous  shaking  until  the  smell  indicates  a 
decided  excess.  Follow  with  5  c.c.  of  concentrated  ammonium 
acetate  to  insure  the  solution  of  any  other  lead  salts.  In  ab- 
sence of  antimony  or  gelatinous  silica,  add  to  the  hot  undiluted 
and  unfiltered  solution,  an  excess  of  about  10  c.c.  of  a  10  per 
cent  solution  of  potassium  chromate,  the  total  volume  being 
less  than  50  c.c.  After  shaking  and  settling  about  five  minutes, 
the  contents  are  to  be  filtered  through  a  close  filter. 

If  these  directions  are  followed,  the  result  will  be  a  granular 
precipitate.  Wash  this  lead  salt  several  times  with  hot  water 
containing  .5  per  cent  acetic  acid,  omitting  the  latter  acid,  how- 
ever, if  the  ores  are  low  in  iron,  or  manganese,  and  if  the  main 
solution  was  strongly  acidified.  Set  the  funnel  over  the  beaker 
and  pass  hot  hydrochloric  acid  (1  :  1)  through  it  until  the  lead 
is  dissolved,  then  wash  the  filter  until  free  from  chromate.  Add 
1  Trans.  A.  I.  M.  E.  35,  367. 


96  ANALYSIS  OF  COPPER 

.5  to  2  grams  of  potassium  iodide,  and  titrate  directly  with  the 
standard  thiosulphate;  of  which  1  c.c.  equals  5  mg.  of  lead. 
By  having  about  50  c.c.  of  (1 :  1)  hydrochloric  acid  in  200  c.c. 
of  the  warm  solution,  any  tendency  to  the  formation  of  lead 
iodide  is  completely  checked,  and  the  end  reaction  is  just  as  sharp 
as  in  a  second  method  devised  for  richer  ores. 

MANGANESE 

23.  In   Slags.  —  Manganese   is   usually   determined,   in   the 
western  States,  by  titrating  the  neutral  solution  of  the  sulphate 
(according   to   Volhard),    with   potassium   permanganate.      Dis- 
solve .5  gram  of  slag  exactly  as  for  iron  (6  and  7,  Chapter  V), 
but  use  less  hydrochloric  acid.     Add  about  5  c.c.  of  nitric  acid 
and  boil  until  most  of  the  chlorine  is  expelled.    All  Lake  Superior 
cupola  slags  are  dissolved  as  in  7  just  quoted,  using  a  beaker 
5.5  cm.  in  diameter  and  12.5  cm.  in  height,  which  is  filled  with 
boiling  water  before  neutralization,  within  one-half  inch  of  the  top. 
Add  a  weighed  excess   (5  to  25  grams)  of  fine  dry  zinc  oxide 
with  rapid  stirring,  as  in  the  analysis  of  steel.     If  a  blank  test 
of  25  grams  of  reagent  requires  more  than  .50  c.c.  of  the  per- 
manganate, the  zinc  oxide  is  not  sufficiently  pure  for  the  purpose. 
For  Western  slags,  dilute  with  hot  water  to  100  c.c.  and  add  the 
emulsion  of  zinc  oxide,  or  the  powder,  until  the  iron  is  com- 
pletely precipitated.     Boil  for  two  minutes   and   titrate  while 
hot,  in  the  presence  of  the  precipitate,  with  potassium  perman- 
ganate.    On   standing   a  few   seconds   after   stirring,   the   mass 
quickly  settles,  and  the  pink  color  at  the  end-point  can  be  easily 
detected  in  the  supernatant  liquid.    The  standard  solution,  used 
for  lime,   may  also  be  taken  for  this  titration;    0.5878   x   its 
calcium  oxide  value  giving  the  value  of  the  solution  in  manga- 
nese,  Mn.     The  titer  in   metallic  iron   may   be   multiplied   by 
.2951  if  desired.    To  make  a  test  of  the  zinc  oxide,  fill  a  beaker 
with  hot  water,  add  1  c.c.  of  sulphuric  acid,  stir  in  the  requi- 
site weight  of  zinc  oxide  used  in  regular  work,  and   titrate  as 
usual. 

24.  Manganese  in  Rich  Ores.  —  According  to  A.  A.  Blair,  we 
may  take  enough  rich  material  to  contain  .05  gram  of  manganese, 
when   using  .1    normal   permanganate.     Fuse    1    gram    of   such 
ore  in  a  large  platinum  crucible  with   10  grams  of  potassium 
bisulphate,  1  gram  of  sodium  sulphite,  and  .5  gram  of  sodium 


ELEMENTS  IN  ORES,   SLAGS,  AND  MATTE  97 

fluoride.  The  heating  should  be  slow  until  effervescence  ceases. 
After  complete  fusion,  cool  the  product,  heat  carefully  with  10 
c.c.  of  sulphuric  acid  (1.84),  Ihen  cool,  dissolve  in  water  and 
make  up  to  a  definite  volume,  from  which,  after  mixing  in  a  dry 
beaker,  an  aliquot  portion  may  be  titrated.  The  slight  amount 
of  barium  sulphate  has  no  influence. 

NOTE.  —  For  the  determination  of  manganese  as  phosphate, 
refer  to  the  analysis  of  brass,  16,  Chapter  XIV. 

25.  Manganese  by  "  Sodium  Bismuthate."  —  This  simple 
titration  process  is  capable  of  great  accuracy,  particularly  with 
iron,  steel,  and  rich  ferruginous  ores.  Originally  devised  by 
Schneider,1  it  has  been  developed  by  Reddrop  &  Ramage,  Bre- 
arley  and  Ibbotsen  in  England  and  improved  by  Blair,2  Brinton,3 
Blum,4  and  the  Society  for  Testing  Materials  in  the  United 
States. 

Titration  with  Permanganate.  —  .015  to  .02  gram  of  manga- 
nese may  be  conveniently  titrated  with  .03  normal  reagent. 
Rich  ores  are  titrated  with  .1  normal  permanganate  (3.1  grams 
of  salt  per  liter). 

The  reagents  employed  in  standardization  of  permanganate 
are:  First,  nitric  acid  diluted  by  mixing  500  c.c.  of  acid  (d.,  1.42) 
and  1500  c.c.  distilled  water.  Acid  for  washing  —  a  3  per  cent 
solution  by  volume.  Second,  potassium  permanganate  for  titration, 
41,  Chapter  III.  Third,  a  solution  of  12.4  grams  of  crystallized 
ferrous  ammonium  sulphate  and  50  c.c.  (of  a  mixture  of  equal 
volumes  of  concentrated  sulphuric  and  phosphoric  acids)  diluted 
to  one  liter.  For  .1  normal  permanganate,  39.2  grams  of  the 
double  salt,  or  27.8  grams  of  crystallized  ferrous  sulphate,  and 
50  c.c.  each  of  sulphuric  and  phosphoric  acids  are  diluted  to  a 
liter.  Test  the  iron  solution  every  day  against  the  permanga- 
nate. If  the  reagent  is  slightly  aged  at  first,  it  will  remain 
practically  unaltered  for  months.  The  same  conditions  should 
prevail  in  the  standardization  and  analysis. 

Standardization.  —  Measure  into  a  200  c.c.  flask  50  c.c.  of  the 
(1:3)  nitric  acid,  cool  in  ice  water  to  less  than  5°  C.,  add  a  very 

1  Dingier  Polytech.  J.  269,  224. 

2  /.  Am.  Chem.  Soc.  26,  793.         3  J.  Ind.  and  Eng.  Chem.  3,  237. 
4  Eighth  Inter.  Congress  of  Chem.,  1,  62. 


98  ANALYSIS  OF  COPPER 

little  sodium  bismuthate,  dilute  with  50  c.c.  of  the  3  per  cent 
acid,  filter  through  an  asbestos  felt  into  a  300  c.c.  flask,  wash 
with  50  c.c.  of  the  3  per  cent  acid,  and  titrate  at  once,  after  the 
addition  of  25  c.c.  ferrous  sulphate  solution.  If  the  felt  is  well 
coated  with  bismuthate,  it  is  unnecessary  to  add  any  to  flask. 
This  gives  the  value  of  the  ferrous  sulphate. 

The  permanganate  may  be  valued:  First,  by  multiplying  the 
iron  value  by  .4919.  Second,  by  the  use  of  a  solution  of  pure 
manganous  sulphate,  in  which  the  manganese  is  determined  by 
evaporating  a  portion  and  heating  for  4  hours  at  450  to  500°  C., 
then  multiplying  the  weight  by  .3638.  Oxidize  and  titrate  1  to  3 
grams  of  this  solution,  which  contains  5.749  grams  of  anhydrous 
sulphate  in  1000  grams.  Or  4.124  grams  may  be  made  up  to 
500  grams  with  distilled  water  and  1  gram  will  contain  .003 
gram  manganese.  A  color  is  given  to  50  c.c.  of  liquid  by  .00005 
gram  of  manganese.  Every  trace  of  nitrous  acid  must  be 
previously  boiled  out  and  the  titration  completed  within  ten 
to  fifteen  minutes  after  filtration.  The  solution  changes  in 
fifteen  minutes  at  40°  C.,  but  will  remain  unaltered  several 
hours  at  5°  C.  A  large  excess  of  bismuthate,  over  .5  to  1  gram, 
is  inadvisable. 

Third  method  for  valuation  of  permanganate,  —  comparison 
with  manganese  in  a  standard  steel  or  ore.  Fourth,  by  specially 
purified  (reagent)  sodium  exalate,  which  has  been  well  dried  in  an 
air  oven  at  100  to  105°  C.  before  use  and  preserved  in  a  small 
glass  stoppered  bottle.  Dilute  the  oxalate  solution  to  75  c.c.  for 
.03  normal  permanganate  and  250  c.c.  for  the  .1  normal  reagent. 
The  initial  temperature  should  be  80  to  90°  C.  and  the  final 
60°  or  higher.  This  is  the  best  method  if  strictly  correct  oxalate 
is  at  hand.  Such  a  correct  salt  may  be  obtained  from  the  U.  S. 
Bureau  of  Standards.  The  value  of  the  permanganate  in  terms 
of  the  oxalate  is  then  to  be  multiplied  by  .16397  to  obtain  the 
equivalent  in  manganese.  The  stronger  permanganate  may  also 
be  used  to  test  the  sodium  arsenite  used  in  the  second  alternative 
method  of  titration  of  steels  and  ores.1 

Titration  by  Sodium  Arsenite.  —  Make  up  a  stock,  solution 
by  heating  in  a  flask  on  the  water  bath  15  grams  of  arsenious 
oxide  (As203)  45  grams  of  sodium  carbonate  and  150  c.c.  dis- 

1  American  Society  for  Testing  Materials.  Official  Method  for  Steel  in 
Year  Book,  1914,  177. 


ELEMENTS  IN  ORES,   SLAGS,  AND  MATTE  99 

tilled  water.  Cool  the  solution  and  make  up  to  1000  c.c.  with 
distilled  water.  A  standard  solution  is  made  by  diluting  300  c.c. 
of  the  " stock  solution"  to  one  liter  and  titrating  against  the  1. 
normal  permanganate  which  has  Seen  standardized  by  the  fourth 
method  above  given.  The  solution  may  be  adjusted  so  that 
1  c.c.  is  equivalent  to  .1  per  cent  of  manganese  when  a  one-gram 
sample  is  taken;  —  formula  47,  Chapter  III. 

Analysis  of  Ores  and  Slags.  —  If  the  ore  dissolves  rather 
easily,  treat  1  gram  with  12  c.c.  of  hydrochloric  acid  (d.,  1.2) 
in  a  120  c.c.  Erlenmeyer  flask,  evaporate  almost  to  pastiness, 
and  then  add  4  c.c.  of  sulphuric  acid  (d.,  1.84).  By  boiling  down 
to  fumes  over  a  free  flame  with  the  flask  in  a  holder,  the  hydro- 
chloric acid  is  so  completely  expelled  that  no  cloud  test  can  be 
obtained  with  silver  nitrate.  This  is  very  essential.  Take  up 
the  residue  with  50  c.c.  of  the  (1:3)  nitric  acid,  cool  at  least 
to  15°  C.,  but  to  5°  C.  for  accurate  work.  Then  add  an  excess 
—  .5  to  1  gram  of  sodium  bismuthate  and  agitate  for  three  to 
four  minutes.  Pour  in  50  c.c.  of  the  cold  3  per  cent  nitric  acid 
(as  in  standardization)  and  filter  through  an  alundum  crucible  or 
asbestos  felt.  Wash  with  about  50  c.c.  of  3  per  cent  acid.  Ti- 
trate at  once  by  potassium  permanganate  after  addition  of  25  c.c. 
ferrous  sulphate  solution,  or  directly  with  the  sodium  arsenite  if 
preferred. 

A  few  ores  will  not  yield  all  the  manganese  to  this  treatment. 
If  the  residue  is  dark,  it  should  be  filtered  off  and  fused  with  a 
very  small  amount  of  potassium  bisulphate.  Metzger  and 
McCrackan  claim  good  results  by  treating  the  sample  with  as 
much  as  10  to  15  c.c.  of  sulphuric  acid.  They  add  subsequently 
1  to  2  grams  of  the  sodium  bismuthate  after  the  hydrochloric 
acid  has  been  removed,  and  boil  the  solution  twenty  minutes  to 
oxidize  the  manganese.  Filter  and  wash  with  about  50  c.c.  of 
the  3  per  cent  nitric  acid  as  before. 

MOLYBDENUM  AND  OTHER  RARE  METALS 

26.  In  copper  refineries,  tests  are  seldom  required  for  any  of 
the  rarer  metals  except  selenium,  tellurium,  gold  or  platinum  in 
copper  or  ores,  and  occasionally  platinum  or  palladium  in 
electrolytic  slimes.  For  the  assay  of  the  precious  metals,  consult 
9,  10,  Chapter  VIII. 

The  determination  of  selenium  and  tellurium  is  taken  up  in 


100  ANALYSIS  OF  COPPER 

10,   Chapter  VII  and  again  in  the  analysis  of    metallic  copper, 
17,  Chapter  XIII. 

The  latest  methods  for  the  identification  of  tungsten,  vana- 
dium, and  other  rare  metals  are  summarized  in  the  "  Report 
on  Rare  Metals  to  the  Committee  on  Analysis,"  —  8th  Inter- 
national Congress  of  Applied  Chemistry  (1913),  pp.  1  to  24. 


CHAPTER  VII 

SPECIAL   DETERMINATIONS   IN   ORES,  SLAGS,    AND   MATTE  — 

CONCLUDED 

FURNACE  REFRACTORIES 
NICKEL  AND   COBALT 

1.  Titration  of  Nickel  in  Matte.  —  For  nickeliferous  matte, 
one  may  use  a  rapid  method  for  the  titration  of  nickel  (and 
copper)  which  involves  the  prior  separation  of  the  copper  as 
sulphide,  and  its  subsequent  titration  in  the  usual  way  by 
potassium  iodide,  as  in  Chapter  IV.  The  nickel  is  titrated  in 
alkaline  sodium  citrate  solution  with  potassium  cyanide.  This 
rapid  assay  is  practiced  by  the  Canadian  Copper  Company. 

To  prepare  for  titration,  weigh  .5  gram  of  matte  into  a  200  to 
300  c.c.  lipless  beaker.  Add  15  c.c.  of  strong  hydrochloric  acid, 
cover,  and  set  the  beaker  on  the  hot  plate.  The  solution  will  be 
complete  in  3  to  5  minutes.  When  the  matte  is  all  dissolved, 
add  a  single  drop  of  nitric  acid,  and  boil  for  a  few  moments. 
Dilute  the  solution  to  about  100  c.c.  with  hot  water  and  pass 
hydrogen  sulphide  gas  until  the  precipitation  of  the  copper  group 
is  complete.  Filter  rapidly  through  a  597  S.  &  S.  filter,  receiving 
the  filtrate  into  a  500  c.c.  griffin-form,  Jena  beaker.  Wash  five 
to  seven  times  with  hot  water,  and  set  the  filtrate  on  a  hot 
plate  to  boil.  Spread  out  the  filter  of  copper  sulphide  against 
the  side  of  the  beaker,  keeping  that  part  of  the  paper  holding 
most  of  the  precipitate,  below  the  rim  of  the  beaker.  Wash  the 
paper  as  free  as  possible  from  the  sulphide,  using  as  little  hot 
water  as  possible.  Now  add  3  to  4  c.c.  of  strong  nitric  acid 
and  place  the  beaker  to  heat.  Remove  any  adhering  copper 
from  the  paper,  or  rod,  by  saturated  bromine  water. 

Evaporate  the  copper  solution  over  a  free  flame,  almost,  but 
not  quite,  to  dryness.  The  yellow  globule  of  sulphur  should 
not  show  any  dark  color.  Wash  down  the  sides  of  the  beaker, 
using,  however,  no  more  than  5  c.c.  of  water.  Add,  drop  by 


102  ANALYSIS  OF  COPPER 


drop,  a  strong  solution  of  sodium  carbonate  just  in  sufficient 
amount  to  form  a  slight  permanent  precipitate.  Redissolve  this 
in  dilute  acetic  acid,  using  a  slight  excess,  keeping  the  volume 
less  than  10  c.c.  Titrate  as  in  method  1,  Chapter  IV,  with 
sodium  thiosulphate  (50,  Chapter  III)  adding  six  times  as 
much  potassium  iodide  (formula  38)  as  there  is  copper  present. 

Nickel.  —  The  nickel  solution  is  treated  while  the  copper  is 
being  prepared  for  titration.  The  nickel  solution  should  be 
boiled  for  2  to  3  minutes  to  expel  the  hydrogen  sulphide  remain- 
ing from  the  copper  precipitation.  While  still  boiling,  and  after 
expulsion  of  the  hydrogen  sulphide,  add  about  1  gram  of  potas- 
sium chlorate  and  boil  for  one  half  minute.  If  the  chlorate  has 
been  added  before  all  the  gas  is  expelled,  sulphur  will  separate 
and  it  is  very  difficult  to  obtain  a  clear  solution.  However, 
prolonged  boiling  with  the  addition  of  more  potassium  chlorate 
will  usually  clear  the  solution.  Cool  slightly  and  add  20  c.c.  of 
sodium  citrate  solution  (47,  —  200  grams  per  liter).  Neutralize 
with  ammonia,  using  a  distinct  excess.  Cool  in  running  water. 
When  the  solution  is  quite  cold,  adjust  the  alkalinity  by 
adding  cold  dilute  hydrochloric  acid,  or  ammonia,  as  required. 
The  correct  degree  of  alkalinity  is  a  distinct  but  small  excess  of 
ammonia. 

The  liquid  is  now  titrated  for  nickel  by  a  modification  of  the 
method  of  T.  Moore.  Add  5  c.c.  of  potassium  iodide  solution 
and  5  c.c.  of  a  solution  of  silver  nitrate  (1  gram  per  liter).  If 
a  permanent  cloudiness  forms  after  the  addition  of  the  potassium 
iodide  and  before  the  addition  of  silver  nitrate,  more  ammonia 
must  be  added  until  the  solution  becomes  quite  clear  again. 
Then  add  the  silver  nitrate,  which  will  cause  a  permanent 
cloudiness.  Run  in  potassium  cyanide  with  constant  stirring 
till  the  solution  is  almost  clear  again.  Now  allow  to  stand  while 
titrating  the  copper,  as  already  described.  Before  that  operation 
is  completed,  the  nickel  will  have  become  cloudy  again.  Care- 
fully add  more  potassium  cyanide  till  the  nickel  solution  becomes 
quite  clear.  These  standard  solutions  are  standardized  against 
matte  which  has  been  analyzed  by  exact  electrolytic  methods. 

NOTE. —  The  potassium  cyanide  solution  contains  24.5  grams 
of  98  per  cent  salt  per  liter  (formula  31,  Chapter  III).  For 
very  accurate  work,  the  amount  of  potassium  cyanide  required 


DETERMINATION  IN  ORES,   SLAGS,   AND  MATTE       103 

to  dissolve  the  precipitate  of  silver  iodide  should  be  deducted 
from  the  total  number  of  cubic}  centimeters  required  to  clear  the 
solution.  (This  usually  amounts  to  about  .15  c.c.) 

For  high  grade  and"  " Bessemer"  mattes,  the  procedure  is 
the  same  except  that  40  c.c.  of  hydrochloric  acid  are  required  in 
dissolving  the  matte.  Five  c.c.  of  the  sodium  citrate  is  sufficient. 
With  the  Bessemer  mattes,  the  potassium  cyanide  must  be  run 
in  very  rapidly  until  near  the  end-point,  otherwise  nickel  cyanide 
may  form.  This  is  difficult  to  dissolve  and  the  end-point  may 
be  passed.  (Zinc  uses  up  cyanide.  Small  amounts  of  cobalt  do 
not  interfere,  but  larger  amounts  spoil  the  titration.) 

2.  Nickel  with  Cobalt  by  Electrolysis.  —  If  copper  is  not  to 
be  determined,  an  ore  may  be  treated  in  a  lipped  beaker  with  a 
mixture  of  acids  and  evaporated  to  strong  fumes  of  sulphuric 
anhydride.  Some  ores,  or  mattes,  may  be  decomposed  very 
easily  by  digestion  with  sulphuric  acid  and  potassium  bisulphate, 
in  the  same  manner  as  for  arsenic. 

The  copper,  etc.,  may  then  be  precipitated  from  the  diluted 
solution  by  hydrogen  sulphide  and  the  remaining  gas  boiled 
out  of  the  filtered  solution.  A  more  rapid  and  satisfactory 
separation,  however,  is  that  by  rapid  electrolysis,  placing  the 
beaker  in  a  Frary  rotary  apparatus.  The  solutions  are  subjected 
to  4  to  4.5  amperes  at  2.75  volts  electrode  tension  when  a  five 
gram  sample  is  tested,  or  3  amperes  for  a  one-gram  sample. 

Conducted  through  a  rheostat,  or  lamp  resistance,  the  current 
from  a  110- volt  circuit  will  deposit  5  grams  of  copper  in  2.5 
hours. 

When  the  iron  percentage  is  low,  the  best  electrolyte  contains 
about  6  to  7  c.c.  of  nitric  acid  and  10  c.c.  of  sulphuric  acid. 

When  the  iron  is  over  10  per  cent,  an  excess  of  nitric  acid  may 
retard  deposition.  If  any  manganese  is  present,  it  may  be  re- 
moved with  the  iron,  or  after  it,  by  boiling  the  faintly  ammonia- 
cal  solution  with  an  excess  of  bromine  or  ammonium  persulphate. 
If  a  separate  assay  for  zinc  is  required,  that  element  may  be 
first  removed  by  rendering  the  solution  faintly  acid  with  acetic 
acid,  adding  a  quantity  of  glacial  acetic  equal  to  one-fifth  of 
the  volume  of  the  solution,  and  saturating  the  cold  solution 
thoroughly  with  hydrogen  sulphide.  If  preferred,  the  Waring 
method  of  precipitation  in  formic  acid  solution  may  be  conducted 


104  ANALYSIS  OF  COPPER 

as  described  under  "zinc."  The  white  sulphide  may  be  colored 
with  a  trace  of  lead  or  copper  sulphide.  The  zinc  is  filtered  out 
and  washed  with  hydrogen  sulphide  water  containing  a  little 
ammonium  acetate,  after  which  the  hydrogen  sulphide  is  boiled 
out  of  the  filtrate.  The  solution  can  now  be  electrolyzed, 
although  a  little  better  result  may  be  obtained  by  adding  5  c.c,. 
sulphuric  acid  and  boiling  down  to  fumes  to  remove  most  of  the 
acetic  and  any  nitric  acid  present.  Neutralize  the  solution  with 
ammonia  (d.,  .9)  and  add  30  c.c.  excess.  The  total  volume 
may  be  100  to  200  c.c.,  according  to  the  amount  of  cobalt  and 
nickel  present. 

If  the  Frary  solenoid  is  used  (Chapter  I),  the  strength  of 
current  may  be  3  to  4  amperes,  with  an  electrode  tension  of  2.5 
volts,  and  the  time  about  one  and  a  half  hours,  or  less.  The 
solution  must  not  become  acid  during  the  deposition.  The 
end-point  is  tested  by  withdrawing  1  c.c.  and  testing  with 
hydrogen  sulphide.  The  current  for  deposition  by  the  slow 
method  is  .5  amperes  per  sq.  dm.  at  2.5  volts  potential.  Two 
accurate  methods  for  preliminary  separation  of  cobalt  arid 
nickel  are  given  later.  The  cobalt  and  nickel  are  then  electro- 
lyzed separately.  The  cathode  deposits  must  always  be  tested 
for  a  trace  of  iron,  and  occasionally  platinum  or  copper. 

3.  Ether  Method  for  Cobalt,  Nickel,  and  Zinc.  —  This  separa- 
tion was  devised  by  H.  Koch  primarily  for  Mansfeld  ores.  The 
separation  of  the  large  quantity  (about  25  per  cent)  of  iron  was 
formerly  made  by  the  "  basic  acetate."  Of  late,  the  well-known 
"ether  method"  of  Rothe  is  used  to  advantage.  The  shaking 
apparatus  of  the  inventor  is  not  used.  The  same  purpose  is 
accomplished  by  a  simple  shaking  cylinder  and  a  removable 
flask  adjoining,  as  shown  in  Fig.  12. 

A  5-gram  sample  of  powdered  crude  ore  in  a  16  cm.  evaporat- 
ing dish  is  moistened  with  water  to  avoid  adhesion  of  the  fines 
to  the  dish,  which  would  occur  if  the  dry  substance  were  heated 
with  acid.  After  decomposing  with  acid,  the  liquid  is  evaporated 
to  dryness  several  times  on  the  water  bath  with  hydrochloric 
acid  to  convert  the  nitrates  to  chlorides,  and  the  separated  sul- 
phur is  burnt  out  by  heating  on  a  small  sand  bath.  The  cooled 
residue  is  treated  again  with  hydrochloric  acid,  evaporated,  and 
taken  up  with  12  to  15  cm.  of  water. 
L  This  concentration  must  be  adhered  to,  since  with  greater 


DETERMINATION  IN  ORES,   SLAGS,  AND  MATTE       105 


dilution  the  later  separation  of  ferric  chloride  is  incomplete. 
The  solution  is  washed  into  the  shaking  cylinder  by  means  of 
40  c.c.  of  hydrochloric  acid  (l:2)^with  50  c.c.  ether  added,  and 
strongly  shaken.  After  ^he  subsidence  of  the  copper  chloride 
solution,  the  etherial  extract  is  drawn  off  by  the  bottle  syphon, 
a  second  equal  quantity  of  ether  added,  and  the  shaking  repeated. 
A  third  similar  extraction  is  sufficient  to  remove  the  last  trace 
of  iron.  (This  operation  may  be  hastened  by  making  one 
ammonia  precipitation  of  the  iron,  followed  by  one  ether  separa- 
tion only.)  The  liquid 
remaining  in  the  shaker 
is  transferred  to  a  750 
c.c.  lipped  beaker,  to  pre- 
cipitate the  copper  and 
arsenic  with  hydrogen 
sulphide.  For  safety,  it 
is  recommended  to  shake 
out  the  ether  extract 
twice  with  some  hydro- 
chloric acid  to  recover  a 
trace  of  nickel  as  chloride, 
which  will  then  be  added 
to  the  main  portion  in  the 
beaker. 

After  filtration,  the 
sulphides  are  evaporated 
to  dryness  with  nitric  and 
sulphuric  acids,  taken  up 
with  water,  the  separated 


Fig.  12.  — Cylinders  for  Ether  Method. 


lead  sulphate  filtered  off,  and  washed  with  dilute  sulphuric  acid. 
In  the  filtrate,  manganese  and  the  small  trace  of  remaining  iron 
are  precipitated  with  ammonia  (and  bromine  water).  Repeated 
precipitation  and  solution  of  the  latter  in  hot  sulphuric  acid 
with  the  addition  of  a  few  drops  of  solution  of  sulphur  dioxide 
is  found  necessary,  as  otherwise  cobalt  remains  in  the  man- 
ganese. The  liquid  is  then  neutralized  with  dilute  sulphuric  acid 
until  the  last  drop  renders  it  slightly  acid  (to  methyl  orange 
indicator),  and  the  zinc  is  precipitated  with  hydrogen  sulphide. 
After  standing  twelve  hours,  the  sulphide  is  filtered  off  with  the 
aid  of  the  hydrogen  sulphide  water,  to  which  some  ammonium 


106  ANALYSIS  OF  COPPER 

sulphate  has  been  added,  and  the  filtrate  is  concentrated  on  the 
water  bath  to  destroy  the  hydrogen  sulphide.  The  solution 
must  first  be  acidified  with  sulphuric  acid,  since  nickel  sulphide 
might  separate  from  it  if  nearly  neutral.  The  concentrated 
liquid  is  then  poured  into  a  1.5-liter  beaker,  saturated  with 
ammonia,  and  electrolyzed  for  the  precipitation  of  cobalt  and 
nickel. 

4.  Separation  of  Cobalt  from  Nickel.  —  Precipitation  with 
potassium  nitrite  is  rather  uncertain,  and  two  more  delicate 
separations  are  now  preferred.  The  first  scheme  is  adapted  to  the 
separation  of  a  little  cobalt  from  much  nickel.  This  is  accom- 
plished by  the  use  of  nitroso-/3-naphthol,  CioH6(NOH) ;  a  method 
due  to  Knorre  and  Illinski.1 

Remove  the  heavy  metals  from  solution,  either  by  hydrogen 
sulphide  or  by  electrolysis,  then  take  out  the  iron  and  alumina 
and  follow  with  a  second  separation  by  ammonia.  A  very  large 
amount  of  iron,  with  little  alumina,  may  be  separated  by  Koch's 
ether  method,  but  if  the  cobalt,  nickel,  and  zinc  are  only  traces, 
as  in  pure  ores  and  high  grade  metal,  two  precipitations  with 
ammonia  are  sufficient.  (See  Waring's  method  for  zinc.)  If 
manganese  is  present,  this  is  removed  by  bromine  or  am- 
monium persulphate.  To  the  nearly  neutral  solution  of  the 
sulphates  of  cobalt,  nickel,  and  zinc  (or  the  solution  of  the  cathode 
deposit  of  combined  elements),  add  4  to  5  c.c.  strong  hydrochloric 
acid,  warm,  and  add  a  hot  saturated  solution  of  the  naphthol 
reagent  in  50  per  cent  acetic  acid,  as  long  as  precipitation 
continues.  Allow  to  settle  for  a  few  hours  at  room  temperature, 
wash  first  with  warm  12  per  cent  hydrochloric  acid  until  all  the 
nickel  is  removed,  then  wash  with  water  to  remove  the  acid. 
The  precipitate  can  be  ignited  with  oxalic  acid  in  a  Rose  cruci- 
ble, finally  reducing  in  hydrogen.  The  best  way,  however,  is  to 
dissolve  in  a  little  nitric  acid  and  3  to  5  c.c.  sulphuric  acid,  and 
evaporate  to  fumes.  Then  dilute,  neutralize  with  ammonia, 
add  30  c.c.  in  excess,  and  electrolyze  with  a  platinum  cathode. 

The  data  for  the  method  are  :  volume  30  to  150  c.c.,  accord- 
ing to  the  amount  of  cobalt;  area  of  cathode  surface  50  or  100 
sq.  cm.;  current  .1  to  .5  ampere,  at  about  2.5  volts  potential. 
With  revolving  anode  or  solenoid,  pass  4  amperes  through  coil 
and  sheet  cathode;  time  about  1  to  1.5  hours.  The  final  test 
1  Ber.  Deutsch.  Chem.  Gesell  (1885),  699. 


DETERMINATION  IN  ORES,  SLAGS,  AND  MATTE        107 

is  made  with  hydrogen  sulphide  water.     Test  the  deposits  for 
purity.  ,   •• 

5.  Separation  of  a  little  NickeJ  from  much  Cobalt  or  Zinc.  - 
The  beautiful  reaction  of  nickel  with  dimethyl  glyoxime,  dis- 
covered by  Tschugaeff  and  Brunck,1  is  made  the  basis  of  the 
method.  This  may  even  be  applied  in  presence  of  the  iron  and 
alumina  by  holding  them  in  solution  with  an  excess  of  sodium 
citrate,  or  tartaric  acid  (2  to  3  grams),  as  in  the  titration  method 
already  described.  It  is  better,  in  this  case,  to  add  also  2  to  3 
grams  ammonium  chloride.  Prepare  the  solution,  ordinarily,  by 
removing  the  heavier  metals,  including  iron,  alumina,  and  man- 
ganese, by  the  separations  already  described  (4).  Then  acidify, 
after  boiling  out  all  hydrogen  sulphide,  until  the  solution  contains 
about  5  c.c.  of  free  hydrochloric  acid.  The  solution  should  be 
diluted  so  that  100  c.c.  does  not  contain  more  than  .1  gram  of 
cobalt ;  and  a  standard  1  per  cent  or  2  per  cent  alcoholic  solution 
of  the  glyoxime  reagent  is  then  added  to  the  boiling  solution  until 
the  amount  is  about  five  times  that  of  the  nickel  and  cobalt. 
Ammonia  is  then  added  until  the  solution  is  slightly  alkaline, 
and  the  precipitate  allowed  to  settle  some  time  on  the  steam 
plate.  The  liquid  is  filtered  hot  through  a  pure  asbestos  felt 
which  has  been  dried  and  weighed.  The  washed  salt  is  dried  to 
constant  weight  at  110°  to  120°  C.  The  compound  has  the 
symbol  CgHnN^Ni,  which  corresponds  to  20.325  per  cent  of 
nickel.  A  method  for  the  recovery  of  the  oxime  is  to  be  found 
in  the  papers  quoted.  The  salt  is  almost  insoluble  in  water  and 
only  very  slightly  soluble  in  alcohol  or  acetic  acid. 

If  accurate  results  are  desired  with  zinc  ore  and  other  rich 
products,  it  is  necessary  to  dissolve  the  pink  precipitate  in 
hydrochloric  acid  (1  :  1),  wash  the  filter,  and  repeat  the  separa- 
tion with  a  little  more  of  the  glyoxime.  The  filtrates  from  the 
nickel  may  then  be  treated  for  the  separation  of  zinc  from  the 
cobalt  by  precipitation  with  hydrogen  sulphide  in  a  formic,  or 
acetic  acid  solution  (as  in  2),  unless  the  cobalt  was  removed 
before  the  nickel  by  method  4. 

Instead  of  weighing  the  nickel  glyoxime,  it  may  be  dissolved 
in  diluted  nitric  or  hydrochloric  acid,  evaporated  to  fumes  with 
5  c.c.  of  sulphuric  acid,  and  the  sulphate  neutralized  with  excess 

1  J.  Soc.  Chem.  Ind.  24,  941;  Zeit.  Angew.Chem.  20,  38,  44;  also  abstract 
J.  Am.  Chem.  Soc.  2,  240. 


108  ANALYSIS  OF  COPPER 

of  ammonia  and  electrolyzed  as  in  2.  The  accuracy  required 
and  the  amounts  or  relative  proportions  of  cobalt,  nickel,  and 
zinc,  should  influence  the  choice  of  the  method  of  separation  of 
these  elements. 

NOTE  (on  Zinc).  —  The  direct  determination  of  zinc  in  slags, 
or  ores,  is  recorded  in  17,  near  the  end  of  this  chapter. 

POTASSIUM  AND   SODIUM 

6.  Potassium  and  Sodium  (with  Lithium)  are  estimated  in 
silicates,  such  as  clay,  slags,  or  ores,  by  removing  all  other 
elements  from  the  solution  successively,  or  by  sintering  in  a 
platinum  crucible  with  an  excess  of  calcium  carbonate  and 
ammonium  chloride,  extracting  with  hot  water  and  precipitating 
any  lime  from  the  extract. 

Solution  Method.  —  Treat  two  grams  of  dried  clay,  or  furnace 
product,  with  an  excess  of  hydrofluoric  acid  and  sulphuric  acid  in  a 
platinum  dish.  In  the  case  of  slags,  it  is  sometimes  advisable  to 
add  nitric  acid.  Heat  gently  without  baking  until  all  free 
sulphuric  acid  is  removed.  A.  H.  Low  recommends  the  direct 
extraction  of  this  residue  with  hot  ammonium  hydroxide.  Such 
treatment  should  be  proved  correct  before  acceptance  with  un- 
known material.  Usually,  the  residue  from  slags,  or  ores,  should 
be  dissolved  in  dilute1  hydrochloric  acid,  and  the  ferric  hydroxide 
and  alumina  removed  by  two  successive  precipitations  with 
ammonia  in  a  platinum  dish.  Filter  and  wash,  then  remove 
any  heavy  metals  by  hydrogen  sulphide,  and  filter  again.  Evapo- 
rate to  dryness  in  a  platinum  dish  and  volatilize  nearly  all  the 
ammonium  chloride.  Dissolve  and  precipitate  calcium  and 
magnesium  by  boiling  with  a  slight  excess  of  ammonia  and 
ammonium  carbonate.  Filter,  evaporate  filtrate,  and  remove 
salts  by  gentle  ignition  as  directed  in  the  next  paragraph. 

Determination  as  Sulphates.  —  After  the  metals  and  alkaline 
earths  are  separated,  evaporate  the  filtrate  or  extract  to  dryness 
in  a  platinum  dish,  and  heat  carefully  at  the  lowest  visible  red 
heat,  or  below  that  point,  until  the  ammonium  salts  are  removed. 
Dissolve  the  residue  in  5  to  10  c.c.  of  hot  water.  If  no  separa- 
tion of  potassium  from  sodium  is  desired,  the  hot  solution  may 
be  tested  with  a  few  drops  of  ammonium  carbonate,  filtered  into 
a  weighed  platinum  crucible,  and  the  solution  and  washings  evapo- 


DETERMINATION  IN  ORES,  SLAGS,  AND  MATTE      109 

rated  again  to  dry  ness  on  the  steam  plate  or  water  bath.  Ignite 
very  gently  as  before  and  aft^r  "cooling  ten  minutes  in  a  desic- 
cator, weigh  the  sulphates.  The,,sulphur  trioxide  in  combination 
may  then  be  found  by  dissolving  the  residue  in  a  very  little 
water,  adding  a  drop  of  hydrochloric  acid,  and  precipitating  with 
barium  chloride.  Allow  to  settle,  filter,  wash,  ignite,  weigh  the 
barium  sulphate,  and  calculate  the  sulphur  trioxide.  Deduct  this 
amount  from  the  total  weight  of  sulphates  to  obtain  the  total 
weight  of  oxides  of  potassium,  sodium  (and  lithium  if  present). 

Determination  as  Chlorides.  —  To  remove  the  small  amount  of 
sulphates  from  the  purified  solutions  of  potassium  and  sodium, 
either  add  barium  acetate,  or  a  slight  excess  of  barium  chloride. 

In  the  former  case,  boil  the  solution,  filter,  wash  out  soluble 
matter,  evaporate  to  dryness,  and  then  heat  to  the  lowest  visible 
red  to  destroy  the  acetates.  Treat  the  residue  with  a  little 
water,  filter  out  any  insoluble  barium  or  magnesium  carbonates, 
add  2  to  3  drops  of  barium  hydroxide  solution,  and  take  again  to 
dryness.  Dissolve  in  5  c.c.  of  water  in  all  cases,  filter  into  a 
weighed  crucible,  concentrate  to  a  low  point,  and  if  the  liquid 
does  not  remain  clear,  filter  into  another  clean,  weighed  crucible. 
Add  two  drops  of  hydrochloric  acid,  heat  very  carefully  to  the 
lowest  perceptible  red,  cool  in  a  dessicator  for  ten  minutes,  and 
weigh  as  chlorides  of  sodium,  potassium,  and  lithium,  if  present. 
Test  the  purity  of  the  residue  by  dissolving  in  5  c.c.  of  water, 
evaporating  with  a  few  drops  of  ammonium  carbonate,  and 
redissolving  in  5  c.c.  of  water. 

If  the  liquid  is  not  clear,  filter  on  a  very  small  paper,  wash 
with  a  few  drops  of  water,  evaporate  in  a  weighed  crucible, 
ignite  gently,  and  weigh  again. 

SEPARATIONS  — POTASSIUM  FROM   SODIUM,   (AND  LITHIUM) 

7.  Potassium  is  separated  from  the  sodium  (or  lithium)  by 
dissolving  the  weighed  chlorides  in  the  least  amount  of  warm 
water,  and  treating  the  clear  solution  in  the  crucible,  or  a  No.  3a 
casserole,  with  sufficient  10  per  cent  solution  of  platinic  chloride 
"  to  convert  all  the  sodium  and  potassium  into  double  salts.  Any 
unchanged  sodium  chloride  would  not  dissolve  in  absolute  alcohol. 
Assuming  the  mixture  to  be  mostly  sodium  chloride,  116.92  parts 
of  sodium  chloride  will  require  195.2  parts  of  platinum,  or  its 
equivalent  as  chloride.  A  slight  excess  of  .5  to  1  c.c.  should  be 


110  ANALYSIS  OF  COPPER 

present  in  addition  to  the  calculated  amount.     Concentrate  below 
the  boiling  temperature  until  the  mass  solidifies  upon  cooling. 

•  Add  a  little  absolute  alcohol  (according  to  A.  H.  Low, 
methyl  is  the  best);  stir  well  with  a  bent  rod  or  wire,  then  filter 
through  a  small  paper  or  a  weighed  asbestos  felt.  Repeat  this 
extraction  and  washing  with  the  alcohol  until  a  pure  golden 
yellow  residue  remains.  Lithium,  if  present,  is  extracted  with 
the  sodium.  William  Crookes  recommends  the  addition  of  J  part 
of  ether  to  the  alcohol.  If  a  dry  filter  is  used,  dry  the  washed 
contents  in  an  oven  at  80  to  90°  C.,  then  transfer  as  much  as 
possible  to  a  watch  glass,  and  wash  the  adhering  salt  with  hot 
water  into  a  weighed  platinum  crucible.  Evaporate  the  solution 
at  a  low  heat,  add  the  rest  of  the  precipitate,  dry  the  whole 
at  160°  C.,  and  weigh  the  potassium  platinic  chloride.  The 
percentage  of  potassium  oxide,  corresponding  to  the  K2PtCl6, 
may  be  found  by  multiplying  by  the  factor  .19376  (or  .30673  for 
KC1).  A.  H.  Low  considers  that  the  older  factor  of  .3056  is  the 
more  correct  one  as  slight  changes  occur  during  evaporation. 
The  sodium  chloride  is  taken  by  difference  and  multiplied  by 
.53028  to  obtain  sodium  oxide,  Na2O.  Lithium  may  be  separ- 
ated as  phosphate.1 

8.  Indirect  Separation.  —  This  is  only  applicable  when  the 
sodium  and  potassium  are  present  in  nearly  equal  amounts. 
First,  determine  the  total  percentage  of  chlorine  in  the  weighed 
chlorides  of  potassium  and  sodium  by  precipitation,  or  by  titra- 
tion,  with  silver  salt.  Finally,  apply  the  rule  of  A.  H.  Low, 
which  is  the  most  simple  form  published.  Subtract  47.56  from 
the  percentage  of  chlorine  in  the  weighed  chlorides  of  potassium 
and  sodium.  Divide  the  remainder  by  13.098  and  the  result 
will  be  the  per  cent  of  sodium  chloride  in  the  mixture  of  the 
two  chlorides.  This  assumes  that  the  lithium  is  negligible. 

The  chloride  of  ammonium,  which  so  often  causes  trouble  by 
creeping  during  evaporation,  may  be  decomposed  very  easily  by 
adopting  a  suggestion  of  J.  L.  Smith.  Evaporate  the  solution 
(after  removal  of  the  lime  and  magnesium  salts)  to  a  low  point, 
transfer  to  a  flask  or  tall  beaker  with  a  very  little  water,  add  3 
to  4  c.c.  of  hydrochloric  acid  for  every  gram  of  ammonium 
chloride  present,  and  heat  at  a  temperature  a  little  below  100°  C. 
until  action  ceases.  Transfer  to  a  small  porcelain  casserole, 

1  Hillebrand,  Bull.  422,  U.  S.  Gcol.  Survey.     (Fresenius,  Quant.  Anal.) 


DETERMINATION  IN  ORES,   SLAGS,   AND  MATTE       111 

evaporate  with  hydrochloric  acid  to  dryness,  treat  again  with  a 
little  ammonium  carbonate,  preceded  by  barium  acetate,  as 
already  described,  and  then  filtdr  back  into  the  weighed  platinum 
dish,  or  crucible. 

9.  Potassium  and  Sodium  (by  the  sintering  method  of  J.  Law- 
rence Smith  l).  —  The  alkaline  metals  in  nearly  all  silicates,  except 
possibly  spinel,  or  some  of  the  silicates  of  heavy  metals,  may  be 
converted  into  soluble  chlorides  by  slow  sintering  in  a  platinum 
crucible  with  an  intimate  mixture  of  pure  ammonium  chloride 
and  calcium  carbonate.  The  alkalies  are  then  leached  out  with 
hot  water. 

Triturate  1  gram  of  the  sample  (in  the  form  of  impalpable 
powder)  with  1  gram  of  pure  ammonium  chloride  in  an  agate 
mortar,  then  mix  with  8  grams  of  calcium  carbonate,  transfer 
to  a  large  platinum  crucible,  and  cover  tightly.  Heat  in  a 
slightly  inclined  position  with  a  very  small  flame  at  a  heat 
which  will  gradually  drive  off  ammonia  gas  but  not  ammonium 
chloride.  When  the  ammonia  is  removed  (which  should  require 
fifteen  to  twenty  minutes),  raise  the  temperature  so  that  the 
lower  half  or  three-fourths  of  the  crucible  are  maintained  for  one 
hour  at  a  dull  red  heat.  Transfer  the  cooled  mass  to  a  large 
platinum  dish  with  100  c.c.  of  hot  water,  boil,  and  break  up  any 
large  particles  with  a  small  pestle.  Filter  and  wash  with  hot 
distilled  water,  boiling  the  residue  with  more  hot  water.  Test 
this  washed  residue  with  excess  of  hydrochloric  acid  to  prove 
that  the  clay,  or  furnace  product,  was  all  decomposed. 

To  the  nitrate,  add  1.5  grams  of  dry  chemically  pure  am- 
monium carbonate,  evaporate  carefully  to  40  c.c.,  add  a  little 
more  carbonate  and  a  few  cubic  centimeters  of  ammonia,  and 
filter  through  a  small  paper.  Wash  the  filter  with  a  little 
water,  and  then  proceed  to  remove  the  last  traces  of  calcium 
and  magnesium  by  evaporation,  gentle  ignition,  and  repeated 
treatment  with  ammonium  hydroxide  and  carbonate.  No  ad- 
dition of  barium  salt  is  necessary,  if  no  sulphates  are  present. 
The  chlorides  are  separated  as  in  the  former  method  (7). 

SELENIUM   AND   TELLURIUM  IN   SLAGS   OR   ORES 

i 

10.   Selenium  and  Tellurium  are  separated  from  large  quan- 
tities of    iron  salts,   and    from  some    heavy  metals,  by  precipi- 
1  Am.  J.  of  Set.  and  Art,  3d  series,  1,  269. 


112  ANALYSIS  OF  COPPER 

tation  with  sulphur  dioxide  in  acid  solution.  The  metals  are 
redissolved,  when  a  separation  of  the  two  is  required,  and  sepa- 
rated from  each  other  by  fractional  precipitation  from  a  hydro- 
chloric acid  solution  by  means  of  sulphur  dioxide.  The  amount 
of  sample  to  be  taken  (5  to  25  grams)  depends  on  the  amount 
of  the  rare  elements  judged  to  be  present  in  the  material  tested. 

Ores  and  Slags.  —  Digest  in  a  mixture  of  strong  nitric  and 
sulphuric  acids  treating  the  insoluble  residue  with  hydrofluoric 
acid,  if  necessary  to  complete  decomposition.  Evaporate  on 
the  water  bath  with  a  slight  excess  of  sulphuric  acid  until 
the  other  acids  are  practically  removed.  In  the  absence  of 
copper  or  similar  metals  a  known  amount  of  ammonium 
nitrate,  potassium  nitrate,  or  zinc  nitrate  should  be  added  before 
evaporation,  sufficient  to  form  double  salts  with  the  selenium 
and  tellurium  and  prevent  any  loss  of  those  elements.  Redis- 
solve  the  salts  in  water  and  filter  out  any  lead  sulphate,  etc.  At 
this  point  there  should  be  no  hydrochloric  acid,  whatever,  in  the 
solution.  Selenium  and  tellurium  may  now  be  separated  com- 
pletely from  iron  and  copper,  or  other  metals,  with  the  exception 
of  gold,  by  heating  to  85  to  90°  C.  and  saturating  the  liquid  with 
sulphur  dioxide  (prepared  according  to  Chapter  III). 

Keep  hot  for  one  hour,  or  long  enough  to  remove  any  yellow- 
ish color  in  the  solution;  finally  cool  the  liquid  while  the  gas 
current  is  passing  and  allow  to  settle  over  night.  Filter  on  a 
pure  asbestos  felt,  made  from  acid- washed,  ignited  material, 
wash  with  dilute  acid,  then  with  water,  dry  at  100  to  105°  C., 
and  weigh.  If  accurate  results  are  desired,  ignite  the  felt  before 
use,  cool,  and  weigh;  then  moisten  with  water,  dry  in  the  oven 
at  100  to  105°  C.,  and  weigh  again.  This  weight  may  be  .5  to 
1  mg.  heavier  than  the  first.  After  drying  and  weighing  the 
dried  precipitate,  ignite  to  redness,  and  obtain  the  elements  by 
loss  as  a  check,  using  the  first  ignited  weight  of  the  felts  for 
comparison. 

In  this,  or  the  following  method  of  separation,  the  filtrates 
from  the  precipitation  of  either  selenium  or  tellurium  should  be 
charged  a  second  time  in  the  same  way  with  sulphur  dioxide  and 
allowed  to  settle,  then  filtered  through  a  second  weighed  filter, 
if  a  trace  of  precipitate  appears. 

Separation.  —  If  selenium  and  tellurium  are  to  be  separated, 
the  first  felt  need  not  be  weighed.  The  reduced  metals  are 


DETERMINATION  IN  ORES,  SLAGS,  AND  MATTE       113 

filtered  off,  then  redissolved  in  a  very  little  strong  nitric  acid, 
the  asbestos  filtered  out,  and  ^the  solution  evaporated  to  dry- 
ness  on  the  water  bath  with  tjhe  addition  of  an  amount  of 
ammonium  or  potassium  nitrate  sufficient  to  combine  with  the 
metals.  If  five  drops  of  sulphuric  acid  are  also  added  to  convert 
the  salts  to  sulphates,  the  subsequent  reduction  takes  place 
quickly.  Dissolve  the  salts  in  90  c.c.  of  hydrochloric  (d.,  1.2) 
and  10  c.c.  of  water,  heat  nearly  to  boiling  for  one  minute  to 
reduce  any  nitrates  and  convert  the  selenium  to  a  lower  chloride. 
Saturate  the  solution  with  sulphur  dioxide,  passing  the  gas  until 
the  solution  is  cold.  Settle  as  before,  filter,  wash  with  90  per 
cent  hydrochloric  acid,  dry,  and  weigh  as  directed  for  the  estima- 
tion of  the  two  elements  together.  The  washing  is  completed 
with  water  to  dissolve  any  sodium  chloride,  but  this  wash  water 
should  not  be  allowed  to  dilute  the  filtrate  until  .a  second  test 
has  been  made  with  sulphur  dioxide  to  insure  the  complete 
separation  of  the  selenium.  To  determine  the  tellurium  in  the 
total  filtrate,  dilute  it  with  four  volumes  of  water,  charge  again 
with  sulphur  dioxide,  and  proceed  exactly  as  directed .  for  se- 
lenium, finally  igniting  the  dried  felt  as  a  check  on  the  weight  by 
drying. 

The  main  solution  of  the  original  sample  may  be  taken  for 
the  estimation  of  arsenic  and  antimony  by  usual  methods. 
See  also  Chapter  XIII. 

11.  The  second  method  for  selenium  and  tellurium  (that  of 
Edward  Keller)  depends  on  the  preliminary  separation  of  the 
rare  elements  from  the  copper  by  repeated  precipitation  with 
ammonia  and  excess  of  ferric  salts.  The  iron  oxide  should  be  at 
least  twenty  times  the  weight  of  the  selenium  and  tellurium. 
Ammonium  ferric  sulphate  is  added  if  necessary,  to  obtain  the 
requisite  amount.  The  copper  should  be  completely  removed 
by  repeated  precipitation  and  filtration,  or  copper  selenide  will 
be  formed  in  the  subsequent  treatment.  This  compound  is 
insoluble  in  sodium  sulphide.  Finally  dissolve  the  iron  hydrox- 
ides in  (1  :  3)  hydrochloric  acid,  dilute  to  400  c.c.,  and  precipitate 
the  selenium,  etc.,  in  the  cold  by  hydrogen  sulphide.  Filter, 
extract  by  repeated  treatment  with  cold,  then  hot,  dilute  sodium 
sulphide  solution,  and  evaporate  the  extract  to  dryness  on  the 
water  bath.  Decompose  the  sulphur  with  fuming  nitric  acid,  or 
with  hydrochloric  acid  and  potassium  chlorate. 


114  ANALYSIS  OF  COPPER 

Evaporate  to  dryness  again  on  the  water  bath,  then  proceed 
as  in  the  previous  method  for  the  precipitation  of  the  selenium 
in  strong  hydrochloric  acid  solution  by  means  of  sulphur  dioxide. 

TIN  IN   ORES  — BY  TITRATION 

12.  Tin,  in  regular  analysis,  is  obtained  with  the  sulphides  of 
arsenic  and  antimony  (method  10,  Chapter  VI).  A.  H.  Low 
has  devised  a  good  volumetric  method,  the  titration  of  stannous 
chloride  by  iodine. 

The  liquid  remaining  in  the  still  after  distillation  of  arsenic 
may  be  taken.  Or  tin  and  antimony  may  be  obtained  from  the 
filtrate  remaining  after  the  precipitation  of  arsenic  by  hydrogen 
sulphide  in  (2  :  1)  hydrochloric  acid.  Dilute  this  filtrate  with 
four  parts  of  water  and  precipitate  the  tin  and  antimony,  then 
filter  and  wash.  Dissolve  the  sulphides  in  a  little  pure  yellow 
ammonium  sulphide,  and  transfer  the  solution  to  a  300  c.c. 
Kjehldahl  flask  with  a  long  neck.  Add  15  c.c.  of  sulphuric  acid 
and  3  grams  of  potassium  sulphate  and  boil  down  to  fumes  of 
sulphur  trioxide.  Now  add  .25  gram  of  solid  tartaric  acid  and 
boil  until  all  sulphur  is  expelled  and  most  of  the  free  acid.  The 
antimony  will  then  be  reduced  to  the  "ous"  condition,  and  is 
ready  for  titration  with  tenth  .normal  permanganate  which  has 
been  standardized  against  pure  antimony. 

Dissolve  the  cooled  residue  in  50  c.c.  of  water  and  10  c.c.  of 
strong  hydrochloric  acid,  boil  out  any  sulphur  dioxide,  add 
10  c.c.  more  of  the  acid,  dilute  to  200  c.c.,  cool  to  room  tem- 
perature and  titrate  directly  for  antimony. 

The  tin  is  determined  by  washing  the  titrated  solution  into 
a  500  c.c.  round-bottomed  flask  with  50  c.c.  of  strong  hydro- 
chloric acid  and  adding  a  reagent  which  will  reduce  the  stannic 
compound  to  stannous  chloride,  ready  for  titration  with  iodine. 
Dilute  to  200  c.c.,  add  1  gram  of  fine  antimony  powder  (chemi- 
cally pure),  and  replace  on  the  steam  bath,  shaking  occasionally. 
A.  H.  Low  uses  a  coil  of  sheet  nickel,  made  from  a  7  x  1  inch 
strip  of  the  pure  metal,  boiling  twenty  minutes  to  reduce  the 
tin  completely  to  the  stannous  condition. 

When  the  tin  is  completely  reduced  by  one  of  these  pure 
metals,  add  a  1  cm.  cube  of  marble  to  the  flask,  cool  rapidly 
in  running  water,  keeping  the  flask  covered,  then  titrate  care- 
fully and  rapidly  with  tenth  normal  iodine,  which  has  been 


DETERMINATION  IN   ORES,   SLAGS,   AND  MATTE        115 

standardized  under  the  same  conditions  against  chemically  pure 
tin  foil.  » 

NOTE.  —  The  foregoing  directions  apply  to  samples  in  which 
the  tin  is  rather  small  in  amount.  When  a  large  amount  of  tin 
is  present,  it  is  most  conveniently  separated  from  antimony,  etc., 
by  Thompson's  oxalic  acid-ammonium  oxalate  method  and 
electrolyzed  (10,  Chapter  VI).  ^ 

TITANIUM 

13.  Titanium  is  determined  in  ores  and  slags  by  separating 
it  from  the  bulk  of  the  iron  and  alumina,  converting  it  with  a 
soda-fusion  to  insoluble  titanate.  The  titanate  is  finally  dis- 
solved and  titanic  hydroxide  precipitated  from  an  acetic  acid 
solution  in  presence  of  sodium  acetate.  The  gravimetric  method 
of  A.  A.  Blair  ("  Analysis  of  Iron"),  may  be  adapted  to  copper 
products,  if  the  sample  is  dissolved  in  acids  as  for  electrolytic 
assaying,  and  the  copper  removed  by  the  electric  current.  In- 
soluble residues  are  fused,  as  directed  in  Chapter  V.  The  copper 
from  blast  furnace  slags  may  be  removed  by  rapid  electrolysis 
in  thirty  to  sixty  minutes.  Treat  the  silica  in  a  platinum  cruci- 
ble with  a  few  drops  of  sulphuric  acid  and  an  excess  of  hydro- 
fluoric acid,  evaporate  the  latter  acid,  and  preserve.  Transfer 
the  electrolyte  and  solution  of  residue  to  a  500  c.c.  beaker, 
evaporate  to  fumes,  and  redissolve  in  150  c.c.  of  water. 
Neutralize  the  liquid  with  ammonium  hydroxide  and  add  50  c.c. 
of  strong  solution  of  sulphur  dioxide,  which  should  redissolve 
any  slight  precipitate.  Now  pour  in  a  clear  filtered  solution 
of  20  grams  of  sodium  acetate  and  acetic  acid  (d.,  1.04)  equal  to 
one-sixth  of  the  total  volume  of  solution.  Boil  for  a  few 
minutes,  allow  to  settle,  filter,  and  wash  with  17  per  cent  acetic 
acid.  Ignite  the  filter  and  contents;  then  fuse  this  insoluble 
residue  with  5  grams  of  sodium  carbonate  for  about  half  an 
hour.  Run  the  fusion  well  up  on  the  side;  cool,  dissolve  in 
water,  and  filter  to  extract  any  soluble  alumina. 

Wash  the  insoluble  sodium  titanate,  re-fuse  it  as  before,  and 
cool  the  crucible.  Then  pour  in  very  gradually  strong  sulphuric 
acid,  finally  warming  the  crucible  slightly  until  the  fusion  is 
dissolved  and  fumes  of  sulphur  trioxide  are  copiously  evolved. 
Pour  the  fluid  contents  into  250  c.c.  of  cold  water  and  wash  out 


116  ANALYSIS  OF  COPPER 

the  crucible.  Add  50  c.c.  of  saturated  aqueous  solution  of  sul- 
phur dioxide  (or  3  c.c.  of  saturated  solution  of  acid  ammonium 
sulphite),  filter  if  necessary,  neutralize  with  ammonia,  treat  the 
clear  and  almost  colorless  liquid  with  the  same  amount  of  so- 
dium acetate  and  acetic  acid  as  before,  and  precipitate  the 
titanium  hydroxide  by  boiling.  If  the  ignited  oxide  is  still  dis- 
colored, repeat  the  fusion  and  precipitation.  Titanium  oxide 
(TiOi)  X  .6005  =  titanium. 

The  manner  of  decomposition  and  number  of  purifications 
for  the  titanic  hydroxide  must  depend  on  the  material  treated. 
If  the  original  "insoluble  matter"  contains  lead  sulphate,  this 
should  be  extracted  with  slightly  alkaline  ammonium  acetate 
before  fusion  of  the  residue  is  attempted. 

14.  Titanium  by  Colorimetric  Assay.  —  The   color  test   de- 
vised by  Weller,1  and  improved  by  H.   L.   Wells  and  W.   A. 
Noyes,2  is  as  follows  : 

Mix  .1  gram  of  ore  with  .2  gram  of  finely  powdered  sodium 
fluoride  in  a  platinum  crucible,  adding  3  grams  of  sodium  bi- 
sulphate  without  mixing.  Fuse  gently  for  two  or  three  min- 
utes until  copious  fumes  are  evolved.  Dissolve  the  cooled  mass 
from  the  crucible  with  15  to  20  c.c.  of  cold  water,  and  filter  and 
wash  with  about  '10  c.c.  of  water.  Treat  any  residue  over  again 
in  the  same  way,  although  the  amount  of  titanium  usually  found 
by  a  second  fusion  is  very  small. 

To  the  solution  add  1  c.c.  of  the  strongest  hydrogen  peroxide 
and  a  few  cubic  centimeters  of  dilute  sulphuric  acid,  when  the 
solution  is  ready  for  comparison  in  a  Nessler  tube  with  a 
standard. 

To  prepare  a  standard  solution,  dissolve  pure  titanic  oxide 
in  hot  strong  sulphuric  acid,  add  dilute  sulphuric  acid  at  first  to 
prevent  precipitation,  then  water  until  1  c.c.  of  the  solution  con- 
tains 1  mg.  of  titanic  oxide,  TiO2-  A  new  volumetric  method 
has  recently  been  devised  by  P.  W.  Shimer.3 

ZINC 

15.  Western  Method  for  Ores  and  Mattes.  —  This  separa- 
tion is  designed  for  rapid  routine  work.     The  principle  involved 
is  the  evaporation  of  the  acid  solution  of  the  sample  and  the 

1  Berichte,  1882,  2592.     2  Trans.  A.  I.  M.  E.  14,  763. 
3  Report  to  Eighth  Inter.  Congress  of  Appl.  Chem. 


DETERMINATION  IN  ORES,   SLAGS,   AND  MATTE        117 

direct  extraction  of  the  zinc  from  the  residues  by  boiling  with  a 
large  excess  of  ammonia  and  apimonium  chloride. 

Add  to  a  .5-gram  sample  in  %<No.  1  beaker  5  c.c.  of  nitric 
acid,  and  cover  with  a  watch  glass.  When  violent  action  ceases, 
add  20  c.c.  of  nitric  acid-potassium  chlorate  mixture.  Boil  five 
minutes,  then  remove  the  cover,  and  evaporate  to  complete  dry- 
ness.  Cool,  add  5  to  10  grams  of  ammonium  chloride,  15  c.c. 
of  ammonia,  and  25  c.c.  of  boiling  water.  Cover  and  boil  two 
minutes.  Filter  and  wash  ten  times  with  a  hot  solution  of  10 
grams  of  ammonium  chloride  in  1000  c.c.  of  water,  containing  a 
few  drops  of  ammonia.  Proceed  as  described  in  the  estimation 
of  "zinc  in  slags,"  beginning  with  the  paragraph,  —  " Conclud- 
ing directions." 

NOTE.  —  If  the  ammonia  precipitate  is  bulky,  dissolve  it  in 
dilute  hydrochloric  acid  and  reprecipitate  with  ammonia,  adding 
ammonium  persulphate  and  bromine  to  oxidize  iron  and  man- 
ganese. Combine  the  filtrates  and  proceed  as  before.  With 
ores  high  in  manganese,  decompose  with  hydrochloric  and  nitric 
acids,  and  when  nearly  evaporated  to  dryness,  stir  in  4  grams 
of  solid  ammonium  chloride  and  proceed  as  in  the  following  slag 
analysis.  If  the  solution,  after  boiling  with  test  lead  to  remove 
copper,  is  yellow  or  brown  from  the  presence  of  chlorine  or 
bromine,  add  1  to  2  grams  of  sodium  sulphite  and  boil  for  a 
minute  more.  Dilute  the  solution  to  200  to  250  c.c.  for  titration. 

Some  silicate  ores  require  a  fusion  to  obtain  all  the  zinc  in 
solution. 

NOTE.  —  Zinc  in  Glass.1  It  has  lately  been  observed  that 
Jena  glass  contains  zinc  compounds  which  are  attacked  by  alkalies. 
Such  ware  should  not  be  used  for  iron  or  zinc  determinations  in 
refined  copper. 

16.  Zinc  in  Slags  is  rapidly  estimated,  after  Western  methods, 
by  placing  .5  gram  of  sample  (or  1  gram  if  low  in  zinc),  in  a 
casserole  and  dissolving  in  3  c.c.  of  water,  5  c.c.  of  hydrochloric 
acid,  and  2  c.c.  of  nitric  acid.  When  the  silica  has  completely 
gelatinized,  stir  in  4  grams  of  ammonium  chloride.  (Some 
chemists  double  this  amount.)  Dehydrate  only  until  the  resi- 

1  E.  and  M.  J.  (1911),  1098. 


118  ANALYSIS  OF  COPPER 

due  crumbles  easily,  because  complete  dehydration  and  baking 
is  liable  to  volatilize  some  zinc  chloride. 

Remove  the  casserole  from  the  plate  and  add  30  c.c.  of 
water.  Bring  to  boiling  and  filter,  washing  well  with  boiling 
water.  To  the  filtrate,  add  .03  gram  of  ammonium  persulphate 
and  10  c.c.  of  saturated  bromine  water  for  every  .01  gram  of 
manganese  in  solution,  then  ammonia  in  slight  excess.  Boil 
two  minutes,  filter,  wash  with  a  mixture  of  1000  c.c.  water, 
100  grams  ammonium  chloride,  and  50  c.c.  ammonia,  and  redis- 
solve  the  precipitate  in  dilute  hydrochloric  acid.  Next,  add 
ammonium  persulphate,  bromine  water,  and  ammonia  as  before, 
bring  to  a  boil,  and  filter.  Combine  the  filtrates  from  the  two 
precipitations. 

Concluding  Directions  for  both  (15)  and  (16).  —  Neutralize 
the  solution  with  hydrochloric  acid,  add  5  c.c.  in  excess  and 
two  grams  of  test  lead,  then  boil  for  fifteen  minutes.  Add  8  to 
10  c.c.  of  hydrochloric  acid  and  titrate,  having  the  temperature 
of  the  solution  about  60°  C.  Use  ammonium  molybdate  solu- 
tion (10  grams  per  liter)  for  an  indicator,  and  potassium  ferro- 
cyanide  as  the  reagent  (32,  Chapter  III). 

The  solution  has  a  value  of  .005  gram  of  zinc  per  cubic  centi- 
meter and  is  standardized  against  pure  zinc,  or  the  oxide.  At 
60°  C.,  the  change  from  bluish  white  to  nearly  pure  white  when 
the  titration  is  nearly  completed,  is  quite  distinct.  In  the  ab- 
sence of  magnanese,  omit  the  persulphate  and  bromine. 

17.  The  Exact  Assay  of  Zinc.  —  The  two  following  methods, 
although  slower,  permit  more  exact  work  than  the  routine  works 
tests  already  described,  especially  with  minute  amounts  of  zinc. 
The  method  of  W.  George  Waring  l  is  sufficiently  accurate  for 
practical  work.  In  dissolving  the  sample,  all  traces  of  nitric 
acid,  or  chlorate,  must  be  removed  by  evaporation  with  hydro- 
chloric and  sulphuric  acids,  successively,  or  by  two  evapora- 
tions with  the  last  acid  to  abundant  fumes.  Dissolve  in  25  to 
40  c.c.  of  water,  add  enough  sulphuric  to  bring  the  free  acid  to 
10  or  15  per  cent  by  volume.  Introduce  a  piece  of  heavy  sheet 
aluminum,  and  boil  ten  minutes,  or  to  complete  reduction. 
Filter  and  wash  through  a  filter  containing  a  piece  of  aluminum 
into  a  beaker  containing  a  strip  of  the  same  metal.  Cool,  add 
a  drop  of  methyl  orange,  and  neutralize  carefully  with  sodium 
1  J.  Am.  Chem.  Soc.  29,  265. 


DETERMINATION  IN  ORES,   SLAGS,  AND  MATTE       119 

bicarbonate  to  a  light  straw  color.  Add  dilute  20  per  cent 
formic  acid,  drop  by  drop,  until- the  pink  color  is  just  restored, 
then  5  drops  more.  Dilute  to  100  c.c.  for  each  .1  gram  of  zinc; 
add  (if  much  iron  is  present)  2  to  4  grams  of  saturated  solution 
of  ammonium  thiocyanate,  remove  the  aluminum,  heat  to  boiling, 
and  saturate  with  hydrogen  sulphide  gas.  Allow  the  pure  white 
mass  to  settle  for  a  few  minutes  and  then  filter. 

A  more  rapid  separation  of  the  sulphide  of  zinc  may  be 
secured  by  passing  the  glass  delivery  tube  through  a  rubber 
stopper,  which  fits  loosely  into  an  Erlenmeyer  flask  containing 
the  solution.  As  soon  as  the  solution  is  saturated  with  hydrogen 
sulphide,  jam  the  stopper  down  while  the  gas  is  passing,  pro- 
ducing a  slight  pressure  which  causes  a  quick  subsidence  of  the 
white  precipitate.  Transfer  the  filtered  and  washed  sulphide  with 
the  paper  to  a  capacious  beaker,  heat  with  8  to  10  c.c.  of  strong 
hydrochloric  acid  until  dissolved,  add  water  and  titrate  the  zinc. 
The  hydrogen  sulphide  must  be  expelled  by  heating  before  titra- 
tion.  A  1  per  cent  solution  of  ammonium  heptamolybdate  is 
recommended  as  the  indicator.  Only  a  part  of  the  cadmium 
deposits  on  the  aluminum,  but  the  percentage  of  this  element 
in  copper  ores  is  generally  so  low  that  it  may  be  counted  with 
the  zinc. 

18.  Proposed  Standard  Method  for  Zinc.  —  F.  G.  Breyer 
recommends  that  1  gram  of  ore  (or  .5  gram  if  over  50  per  cent 
zinc)  be  dissolved  in  a  tall  150  c.c.  lipless  beaker,  covered,  by  10 
c.c.  of  hydrochloric  acid  and  a  little  water.  (Jena  glass  should 
be  rejected  from  such  work,  as  it  contains  zinc.)  A  sample  is 
taken  at  the  same  time  and  dried  at  110°  C.  for  moisture  deter- 
mination. After  boiling  one-half  hour  remove  the  cover,  add 
10  c.c.  of  sulphuric  acid,  and  evaporate  slowly  to  strong  white 
fumes,  breaking  up  the  silica  if  necessary.  Then  dilute  to  about 
40  to  50  c.c.  and  add  about  1  gram  of  aluminum  powder,  cover, 
and  boil  until  colorless,  which  requires  ten  to  fifteen  minutes. 

If  the  cadmium  in  ores  is  uniformly  less  than  .05  per  cent,  it 
is  allowed  for,  or  counted  with  zinc,  as  in  17.  A  separation  of 
cadmium  should  be  made,  if  an  accurate  result  on  zinc  is 
desired.  (Method  14,  Chapter  VI,  also  precedes  this  separation). 

(a)  The  cadmium  not  reduced  by  aluminum  is  thrown  down 
by  hydrogen  sulphide  after  adding  5  c.c.  of  (1  :  1)  sulphuric  acid 
and  diluting  to  100  c.c.  Neutralize  until  cadmium  sulphide 


120  ANALYSIS  OF  COPPER 

appears,  and  heat  to  70  to  90°  C.  Filter,  wash  with  cold  8 
per  cent  sulphuric  acid,  then  with  hot  water,  first  closing  the 
paper  with  precipitated  sulphur.  Dissolve  and  evaporate  to 
fumes  with  sulphuric,  adding  any  reduced  cadmium. 

(b)  The  cadmium  may  then  be  electrolyzed,  after  the  addi- 
tion  of    1    c.c.    of  (1  :  1)   sulphuric    acid  to   the    carefully  neu- 
tralized solution. 

Total  volume  100  c.c.;  current  .8  to  1  ampere  per  square 
decimeter  of  cathode  surface;  time  one  and  one-half  hours  at 
2.95  to  3.05  volts  with  a  coppered  cathode,  —  the  best  is  a  gauze 
electrode  coated  with  cadmium  over  copper,  which  may  be  used 
repeatedly. 

(c)  The  zinc  solution  is  then  boiled  to  remove  hydrogen  sul- 
phide,  exactly  neutralized  with  potassium   hydroxide,   finishing 
with  sodium  bicarbonate,  and  then  made  acid  again  with  2  to 
4  c.c.  of  5  per  cent  sulphuric  acid  in  excess  for  each  100  c.c.  of 
solution.     The  zinc  is  finally  precipitated,  redissolved,   and  ti- 
trated as  in  17,  with  potassium,  ferrocyanide  having  a  value  of 
10  mg.  of  zinc  per  cubic   centimeter.     This  solution  has  a  tem- 
perature coefficient  sufficient  to  decrease  the  factor  .2  per  cent 
for  5°  C.  rise  in  temperature;   hence  any  variation  between  the 
temperature  of  standardization  and  actual  analysis    should    be 
corrected. 

This  modification  differs  from  Waring' s  method  (which  the 
author  prefers)  in  the  fact  that  sulphuric  acid  is  used  instead  of 
formic,  and  the  aluminum  is  taken  as  a  powder. 

19.  European  Method  for  Zinc  in  Mansfeld  Ores.  —  These 
ores  carry  nickel  and  cobalt  with  the  zinc.  Hermann  Koch 
separates  the  former  elements  from  zinc  by  direct  precipitation 
with  hydrogen  sulphide  in  a  faintly  acid  sulphate  solution,  as  in 
18.  The  purified  sulphide  is  finally  ignited  in  a  Rose  crucible 
in  a  stream  of  hydrogen. 

The  author  also  recommends  titration  by  standard  sodium 
sulphide,  shaking  the  solution  in  a  flask  with  a  layer  of  carbon 
tetrachloride. 

The  sodium  sulphide  is  protected  from  oxidation  by  keeping 
the  space  above  the  stock  solution  charged  with  illuminating 
gas  (meeting  an  objection  of  Mr.  Waring),  but  the  process,  al- 
though claimed  to  be  well  adapted  to  lead,  has  not  found  favor 
in  the  United  States. 


DETERMINATION  IN  ORES,   SLAGS,  AND  MATTE      121 

FURNACE  REFRACTORIES 

20.  Beach-sand,   or  .^quartz  for  converter  lining,   containing 
over  95  per  cent    silica,  is   treated   to   best  advantage   if   the 
silica  is  at  once  volatilized.1 

Weigh  at  least  1  gram  of  the  fine  powder  (ground  in  agate), 
and  treat  it  in  a  weighed  platinum  crucible,  with  a  few  drops  of 
strong  sulphuric  acid,  placing  the  crucible  upon  a  pipe-stem 
triangle,  resting  on  a  wire  gauze.  Add  gradually  enough  hydro- 
fluoric acid  to  dissolve  the  silica,  then  evaporate  in  the  hood 
with  the  heat  of  a  Bunsen  burner,  and  heat  to  redness  long 
enough  to  decompose  the  ferric  sulphate.  Weigh  the  residue, 
and  later  correct  it  by  deducting  the  weight  of  sulphur  trioxide, 
calculated  to  exist  in  combination  with  the  calcium,  magnesium, 
and  alkalies.  Fuse  the  slight  residue  with  sodium  carbonate  and 
determine  the  alumina,  calcium,  and  magnesium  oxides  by  the 
regular  methods  given  for  slags  in  method  10,  Chapter  V. 

The  determination  of  alkaline  metals  is  given  in  a  succeeding 
paragraph,  but  for  ordinary  purposes  it  is  sufficient  to  estimate 
the  bases,  already  mentioned,  and  deduct  their  sum  from  100 
per  cent  to  obtain  the  silica. 

21.  Semi-fusible  Sand,  of  lower  silica  content  (90  to  95  per 
cent),  derived  from  weathered  feldspathic  rock,  is  employed  at 
Lake  Superior,   Michigan,   and  elsewhere,  to  render  pure  sand 
more  fusible.     Such  sand  requires  fusion  with  dry  sodium  car- 
bonate  and   a  trace   of  sodium   nitrate,   after  which  the  mass 
should  be  dissolved  in  dilute  hydrochloric  acid  and  dehydrated 
twice  by  evaporation  to  dryness  with  an  intermediate  filtration. 
The   bases    are  determined  as   in  the  analysis  of    reverberatory 
slags  and  Calcines,  Chapter  V,  or   as   in   the  analysis  of   clays. 
Alkalies   are   determined   by  methods  6  to  9,  Chapter  VII. 

ANALYSIS   OF  CLAYS 

22.  Fire-clay,  or  fusible  clays,  are  usually  dried  before  use 
as  a  fettling  material,   and  then  ground.     An  average  sample 
may  then  be  taken. 

Any  residual  moisture  is  determined  by  drying  a  sample 
at  100  to  105°  C.  To  obtain  the  loss  on  ignition,  which  is  mostly 

1  Original  method  due  to  A.  A.  Blair. 


122  ANALYSIS  OF  COPPER 

due  to  water  of  composition  in  the  hydrated  silicates,  ignite  a 
sample  of  1  gram  in  a  platinum  crucible  to  a  constant  weight. 

For  bases,  fuse  1  gram  of  dried  clay  with  10  grams  of  sodium 
carbonate  and  a  pinch  of  pure  sodium  nitrate.  Transfer  the 
fused  mass  by  means  of  hot  water  to  a  platinum  dish.  Clean  the 
crucible  with  a  little  hot  hydrochloric  acid,  make  the  solution 
acid  with  hydrochloric  acid,  and  evaporate  twice  to  dryness  at 
100  to  105°  C.  with  the  addition  of  dilute  hydrochloric  acid 
before  the  second  evaporation.  Dissolve  in  10  c.c.  of  the  same 
acid,  add  50  c.c.  of  water,  filter  the  silica  on  an  ashless  paper, 
ignite,  and  weigh.  Treat  the  weighed  residue  with  two  drops  of 
sulphuric  acid  and  an  excess  of  hydrofluoric  acid,  evaporate, 
ignite,  and  weigh  again.  Deduct  the  weight  of  the  last  residue 
from  that  of  the  total  siliceous  matter  to  obtain  the  true  weight 
of  pure  silica.  Fuse  the  last  residue  with  the  least  possible 
amount  of  potassium  bisulphate,  or  sodium  carbonate,  and  re- 
turn the  solution  of  the  melt  to  the  main  solution  of  the  bases. 
Determine  the  bases  by  the  methods  recommended  for  slags  and 
ores,  5-12,  Chapter  V.  If  potassium  and  sodium  are  required, 
refer  to  methods  6-9.  If  extremely  accurate  results  are  desired, 
the  work  should  be  performed  in  platinum  dishes.  It  would  be 
necessary  to  grind  all  such  refractory  siliceous  material  in  agate, 
or  in  porcelain  ball-mills,  after  it  leaves  the  crusher. 

CHROMIUM  COMPOUNDS 

23.  Complete  Analysis.  —  Chromium  and  iron  in  chromite  or 
furnace  refractories  may  be  estimated  by  the  volumetric  method 
of  A.  G.  McKenna.1  The  material  should  be  ground  (after 
coarse  crushing)  in  an  agate  mortar  to  pass  a  sieve  of  100 
meshes  to  the  linear  inch  (40  per  cm.).  Fuse  .5  gram  of  the 
powder  in  a  nickel  crucible  at  a  low  red  heat  for  one  minute,  or 
until  decomposed,  and  determine  the  chromate  in  the  solution 
of  the  fusion  by  method  15,  Chapter  VI. 

Iron.  —  Dissolve  the  iron  from  the  insoluble  residue  with 
(1:10)  sulphuric  acid,  reduce  it  with  zinc  or  with  slight  Excess  of 
stannous  chloride  and  titrate  with  potassium  permanganate 
(6-7,  Chapter  V.)  Calculate  to  ferrous  oxide,  FeO. 

Silica  and  bases  may  be  determined  in  a  second  sample 
by  a  modification  of  the  method  of  McKenna.  Fuse  .5  gram 

1  Proc.  Eng.  Soc.  W.  Pa.,16, 119  —  Methods  of  Iron  Analysis,  Phillips,  156. 


DETERMINATION  IN  ORES,   SLAGS,  AND  MATTE       123 

of  the  powder  in  a  silver  crucible  with  4  grams  of  pure  sodium 
peroxide.  Just  as  soon  as  fusion  is  complete,  cool  the  crucible 
and  dissolve  the  melt  in  water  ig.  a  3a  casserole.  (If  alumina  is 
to  be  separated  from  chromium  as  noted  in  the  final  paragraph 
below,  boil  for  ten  minutes  to  destroy  peroxide  which  might  cause 
premature  reduction  of  the  chromium  after  the  solution  is  acidi- 
fied.) Filter  the  liquid  from  the  undissolved  portion.  The  residue 
contains  iron  oxide,  magnesia,  a  little  silver,  and  silica.  The  filtrate 
should  contain  the  chromium,  alumina,  and  most  of  the  silica. 

Residue.  —  Dissolve  the  insoluble  portion  in  an  excess  of  ni- 
tric' and  sulphuric  acids,  cleaning  the  crucible  with  the  latter 
acid.  Evaporate  to  fumes,  take  up  with  water,  and  filter  off 
the  silica.  To  the  solution  add  two  or  three  drops  of 
hydrochloric  acid  and  filter  off  any  trace  of  silver  chloride  which 
may  separate  on  stirring.  Precipitate  the  iron  hydroxide  by 
ammonia,  ignite,  and  weigh.  The  ferric  oxide  may  contain 
traces  of  alumina.  To  the  filtrate  add  ammonium  oxalate, 
filter  off  the  calcium  oxalate,  and  remove  the  magnesium  as  phos- 
phate (10,  Chapter  V).  Nickel  and  zinc,  if  present,  are  separated 
before  the  lime,  the  nickel  by  dimethyl  glyoxime  (5,  Chapter  VII), 
and  the  zinc  by  saturating  the  filtrate  with  hydrogen  sulphide 
after  acidifying  with  a  slight  excess  of  acetic  acid. 

Filtrate  from  Peroxide  Fusion.  —  Acidify  the  solution  of 
sodium  aluminate,  chromate,  and  silicate  with  hydrochloric  acid 
and  evaporate  to  dryness.  Dilute,  filter  off  the  silica,  and 
evaporate  again  to  dehydrate  the  last  traces  of  silica.  Ignite 
the  washed  silica  with  that  obtained  from  the  insoluble  residue. 
Test  its  purity  with  hydrofluoric  acid.  Precipitate  the  alumi- 
num and  chromium  as  hydroxides  from  a  boiling  solution  with 
a  slight  excess  of  ammonia.  Filter,  wash  thoroughly,  ignite  and 
weigh.  To  obtain  the  alumina,  deduct  the  weight  of  chromium 
sesquioxide  calculated  from  the  titration. 

An  approximate  separation  of  aluminum  from  chromium  may 
be  effected,  if  desired,  by  treating  the  alkaline  filtrate  from  the 
original  fusion  as  follows :  —  Acidify  with  nitric  acid,  evaporate 
to  dryness  on  a  water  bath,  dissolve  in  nitric  acid,  dilute,  and 
filter  off  the  silica.  Test  the  filtrate  for  silver  with  one  drop  of 
hydrochloric  acid,  filter  and  wash.  Make  the  solution  slightly 
ammoniacal,  warm  until  coagulated,  and  filter,  washing  four 
times  back  and  forth  from  beaker  to  filter  with  water  and  a 


124  ANALYSIS  OF  COPPER 

trace  of  ammonia.  Ignite  and  weigh.  Reduce  chromium  in 
the  filtrate  by  evaporating  to  dryness  with  an  excess  of  hydro- 
chloric acid. 

Take  up  with  hydrochloric  acid  and  evaporate  again 
to  remove  all  the  nitric  acid  and  completely  reduce  the  chro- 
mium. Finally,  throw  down  the  chromium  hydroxide  with  an 
excess  of  ammonia. 


CHAPTER  VIII 

FIRE   ASSAYING   FOR   LEAD,    SILVER,   GOLD,  AND   PLATINUM 
IN  ORES  AND  FURNACE  BY-PRODUCTS 

Commercial  Requirements.1  —  In  most  transactions  involving 
the  purchase  and  sale  of  argentiferous  copper  materials,  the  so- 
called  "commercial  assay"  governs  financial  settlements.  The 
term  commercial  assay  means  the  usual  fire  or  combination  assay, 
without  including  corrections  for  gold  or  silver  which  could  be 
recovered  by  reassaying  slags  and  cupels. 

Corrected  assays  are  made  only  when  contracts  require  them. 
Deductions  for  refining,  or  refining  charges,  are  generally  based 
on  commercial  assays,  and  these  bear  a  very  constant  ratio  to 
corrected  assays  for  any  given  material.  (This  ratio  is  so  uni- 
form that  E.  Keller  uses  the  slag  and  cupel  correction  for  a 
month's  run  on  Anaconda  anodes  as  the  correction  for  the  next 
month's  copper.)  Corrections  are  obtained  by  reassaying  the 
cupels  and  slags,  and  adding  the  silver  and  gold  recovered. 
Manuals  of  assaying  have  described,  in  detail,  the  testing  of  true 
gold  or  silver  ores.  This  chapter  treats  only  of  native  copper, 
or  copper  ores  smelted  at  copper  reduction  works,  and  the 
furnace  by-products. 

Systems  of  Assay  Weights.  —  On  the  European  continent 
assay  results  are  calculated  in  "grams  per  kilo/'  or  "grams  per 
metric  ton  of  1000  kg."  1  metric  ton  equals  2204.6  pounds 
avoirdupois. 

In  Great  Britain,  we  find  results  expressed  in  Troy  ounces 
per  ton  of  2000  pounds,  the  long  ton  of  2240  pounds  being  often 
used. 

Assayers  in  the  United  States  have  almost  entirely  adopted 
the  so-called  "Assay-ton  system."  The  concise  definition  of 
Dr.  A.  R.  Ledoux  explains  the  system. 

"Silver  and  gold  are  reported  in  Troy  ounces  (of  480  grains  each), 
per  ton  of  2000  pounds  avoirdupois.  One  such  ton  contains  29,166.66 

1  A.  M.  Smoot,  personal  communication. 


126  ANALYSIS  OF  COPPER 

ounces  Troy.  The  ' assay-ton'  (A.  T.),  a  weight  introduced  by  Dr.  C.  F. 
Chandler,  contains  29,166.66  milligrams;  hence  each  milligram  of  silver  or 
gold,  obtained  by  assay  from  1  A.  T.  of  sample,  represents  1  ounce  Troy  per 
ton  of  2000  pounds.  The  ounce  Troy  is  equivalent  to  31,103.49  mg.,  and 
one  ounce  per  ton,  as  above,  equals  34.286  grams  per  metric  ton  or  .00343 
per  cent." 

ASSAY  OF  LEAD 

1.  The  Dry  Lead  Assay.  —  According  to  "  Western  practice," 
a  lead-flux  stock  mixture  is  made  up  in  large  quantity  as  follows  : 
sodium  bicarbonate  64  parts,  powdered  borax  16  parts,  argols 
(crude  cream  of  tartar)  14  parts.    Mix  10  grams  of  sample  with 
20  grams  of  "flux,"  cover  with  10  grams  more  flux.     Put  in  3 
nails,    then    a    cover  of    1.5    inches   (3.8    cm.)   of    salt  (sodium 
chloride).     Oxide  and  carbonate  ores,  as  well  as  those  high  in 
zinc,   require  the  addition  of  some  borax  glass,   but  only  the 
amount  necessary  to  give  a  good  pouring  fusion  must  be  used  or 
the  slag  will  be  too  acid  and  carry  off  lead.     Place  the  crucible 
in  a  good  hot  muffle  and  close  the  door.     As  soon  as  the  salt 
cover  is  melted  and  the  argols  begin  to  flame,  shut  off  the  draft 
and  lower  the   heat   to   a  little   below   scorifying  temperature. 
Keep  at  this  heat  until  flaming  of  argols  ceases,  then  raise  the 
temperature  to  the  highest  heat  possible,  and  pour.     The  pot 
furnace  may  be  used  instead  of  muffles.     The  "wet  methods," 
especially   titration,    involve   more   work,    but    are    much    more 
accurate  than  the  fire  assay,  especially  on  cupriferous  ores. 

GOLD,  SILVER,  AND  PLATINUM 

2.  Gold  and  Silver,  in  Colorado,  are  generally  assayed  by 
the  scorification  method,  but  in  Arizona,  California,  Michigan, 
and  Montana   ores    are  more  often  fired  in  crucibles.     If  the 
copper  percentage  is  sufficient  to  class   a    sample  with  copper 
ores,  the  calculated  niter  assay,  or  the  excess  litharge  flux,  is 
adopted.     If  the  ores  are  low  in  copper,  arsenic,  or  antimony, 
good  results  may  be  obtained  by  the  method  of  Aaron,  using 
iron  nails  as  the  desulphurizer. 

If  fused  sodium  carbonate  is  employed,  take  only  60  per  cent 
of  the  amount  in  the  table.  An  assay  furnace  has  been  described 
in  Chapter  I.  The  best  crucibles  for  gold  and  silver  assay  are 
the  Denver,  or  Battersea,  but  the  cheaper  Hessian  sand  cruci- 
ble is  favored  for  the  fire  assay  of  native  copper,  where  it  is 


ASSAYING  FOR  LEAD,   SILVER,   GOLD,   PLATINUM      127 

necessary  to  clean  the  button  from  iron.  Place  the  assays  in 
the  muffle,  or  pot  furnace,  at  a  good  red  heat,  fill  in  coke  around 
the  crucibles,  and  bring  the  heat  up  gradually  until  there  is  no 
more  danger  of  loss  by  learning,  lifter  which  the  tests  are  brought 
up  to  a  high  heat  and  quiet  fusion,  then  poured  into  iron  molds, 
the  insides  of  which  are  painted  with  iron  oxide  (crocus). 

As  this  account  presupposes  some  knowledge  of  principles, 
the  reader  is  referred  to  Brown's  "  Assaying,"  ninth  edition,  page 
185,  or  to  Lodge's  "  Notes  on  Assaying,"  for  the  general  details 
of  melting  and  cupellation.  Less  reducer  is  required  if  the 
crucibles  are  kept  covered  in  the  furnace.  The  proportions  of 
flux  and  reducer  must  be  adjusted  to  the  conditions  of  the 
sample  and  firing.  The  amount  of  sulphides  is  roughly  deter- 
mined, accordingly,  by  vanning  some  of  the  sample.  If  the 

FLUX  FOR  IRON  NAIL  METHOD 


Crucible  Assay 

A-l 

Quartz 
oxidized 

A-2 

Ore  with 
little  iron 
sulphide 

B 

Half  gangue 
Half  sulphide 

C 
Mostly  iron 
sulphide 

Sample  taken 

3  A.  T. 

1  A.  T. 

1  A.  T. 

1  A.  T. 

Litharge  
Sodium  bicarbonate. 
Borax  glass  
Argols   (or  75  %  of 
flour)   

100.  gr. 
125  fused 
50 

2-3 

35-50  g. 
60-100 
5-30 

2 

35  g. 
60 
10 

35  g. 
50 
20 

Silica,  fine  

5 

10 

Iron  20  penny  nails 

1 

4 

Cover  —  2.5  to  3.8  cm.  of  salt,  sodium  chloride. 

lead  buttons  are  hard  enough  to  crack,  or  split,  when  squared 
on  the  anvil,  they  should  be  scorified  before  cupellation  with 
the  addition  of  a  little  more  lead,  unless  the  button  is  very  large. 

Cupellation.  —  The  lead  buttons,  when  rendered  sufficiently 
pure  by  scorification,  are  dropped  into  hot  marked  cupels  placed 
in  the  hot  muffle,  the  door  closed  and  the  assays  brought  to  the 
front,  or  the  heat  lowered  as  soon  as  the  assays  are  melted  down. 

The  lead  is  allowed  to  vaporize  in  the  open  muffle  at  a  heat 
low  enough  to  cause  the  cupels  to  " feather"  nicely.  (It  is  best 
to  round  off  the  corners  of  the  lead  buttons,  which  will  weigh, 


128  ANALYSIS  OF  COPPER 

according  to  the  ore  and  flux,  from  10  to  20  grams.)  When  the 
lead  is  nearly  gone,  and  the  play  of  colors,  known  as  the  "blick," 
is  about  to  appear,  the  button  becomes  round  and  the  litharge 
commences  to  swim  over  the  small  button.  At  this  point  the 
button  should  be  pushed  into  the  hottest  part  of  the  muffle. 
Soon  after  the  blick,  the  assay  should  be  withdrawn  from  the 
muffle,  covering  the  bead  with  an  old  cupel,  if  necessary,  to  pre- 
vent any  sprouting  of  the  button.  It  is  never  safe  to  accept  a 
sprouted  button.  Cement-lime,  or  "Brownite"  cupels  are  much 
used  at  present,  instead  of  bone-ash,  especially  by  Lake  Superior 
refineries  for  the  direct  cupellation  of  silver  chloride  in  the  assay 
of  anodes,  Chapter  IX.  These  cupels  must  be  ignited  at  a  low 
yellow  heat  and  brought  to  a  low  red  heat  before  the  lead  but- 
tons are  introduced,  in  order  to  prevent  spitting.  With  this 
precaution,  this  cupel  will  absorb  less  silver  than  bone-ash, 
particularly  when  silver  chloride  is  directly  cupelled  with 
powdered  lead.  The  calcium  oxide  of  the  cupel  assists  in  the 
prompt  reduction  of  the  chloride,  preventing  loss  by  volatilization. 

Weighing  and  Parting  for  Gold.  —  The  beads  are  separated  by 
forceps,  brushed  with  a  stiff  brush,  and  any  adherent  material 
removed  by  very  careful  picking  with  a  needle,  or  by  dipping 
the  buttons  in  very  dilute  hydrochloric  acid.  The  weights  on 
a  gold  balance  should,  of  course,  be  carefully  adjusted  from  time 
to  time  to  detect  any  variation.  If  only  gold  is  to  be  weighed, 
the  beads  are  transferred  at  once  to  small  porcelain  crucibles,  or 
test  tubes,  and  heated  nearly  to  boiling  with  dilute  nitric  acid. 
Assay ers  vary  in  the  strength  of  acid  specified.  The  Western 
contributing  chemists  recommend  an  acid  as  dilute  as  1  volume 
of  acid  to  9  of  water  for  the  first  treatment.  When  the  action 
ceases,  a  few  drops  of  strong  nitric  acid  (d.,  1.42),  are  added  and 
the  warming  continued  for  a  few  minutes.  The  crucible  is  then 
filled  with  hot  water  repeatedly,  tapped,  and  poured  off. 

Estimation  of  Platinum.  —  This  metal  dissolves  quite  com- 
pletely in  nitric  acid  in  the  presence  of  8  parts,  or  more,  of 
silver.  The  silver  beads,  containing  platinum,  are  parted  by 
boiling  for  about  fifteen  to  twenty  minutes  with  a  little  strong 
sulphuric  acid.  The  purified  gold  and  platinum  are  washed, 
annealed,  weighed,  then  remelted  with  8  to  10  parts  of  pure 
silver  foil,  and  parted  a  second  time  with  nitric  acid  (1:1)  to 
dissolve  the  silver  and  platinum,  leaving  the  gold  for  weighing. 


ASSAYING  FOR  LEAD,   SILVER,   GOLD,   PLATINUM      129 

A  more  accurate  special  method  is  given  in  the  latter  part 
of  this  chapter. 

2a.  Excess  Litharge-Assay  for  Gold.  —  Ledoux  &  Co.  assay 
rich  sulphides,  mattes,  or  slags  as  follows  :  Mix  one-half  assay 
ton  (A.  T.)  of  sulphides  in  a  G  crucible  with  500  grams  of  flux, 
composed  of  litharge  40  parts,  soda  4  parts,  silica  4  parts, 
adding  a  salt  cover.  For  slags  use  only  300  grams  of  flux. 
Fuse  for  about  thirty  minutes,  starting  at  a  low  heat  and  rais- 
ing the  temperature  gradually  during  the  first  twenty  minutes, 
then  withdraw  the  assay,  cool  and  break  the  crucible.  The 
lead  button,  reduced  by  the  sulphur  and  iron,  will  weigh  from 
80  to  100  grams.  Scorify  the  button  to  about  30  grams 
weight  before  cupellation.  Cupel  and  part  as  in  the  scorifica- 
tion  method  for  gold  (method  4). 

When  the  material  for  assay  is  low  in  gold,  make  a  number 
of  crucible  fusions,  using  .5  A.  T.  charges  of  ore  in  each.  After 
reducing  the  large  lead  buttons  by  scorification  to  about  30 
grams  each,  unite  several,  and  scorify  to  a  single  button  of  a 
size  suitable  for  the  cupel.  Usually,  four  crucible  fusions,  repre- 
senting two  assay  tons,  are  sufficient. 

If  the  material  under  assay  is  deficient  in  silver  as  compared 
with  gold,  some  silver  may  be  added  to  the  crucible  or  scorifier. 
A  very  large  amount  of  litharge  flux  is  essential  in  assaying 
matte  and  ores  rich  in  copper.  This  method  is  very  satisfactory 
for  gold,  but  it  cannot  be  relied  upon  for  silver.  For  mattes, 
the  combination  method  5  is  generally  the  most  satisfactory. 
When  silver  is  added,  it  should  be  six  or  seven  times  as  much  as 
the  gold  present. 

Cupellation.  —  The  cupellation  is  made  at  a  low  heat  and 
the  beads  parted  for  gold  as  described  in  the  combination 
method  for  metallic  copper  (5,  Chapter  X). 

The  addition  of  silver,  as  recommended,  reduces  the  slag 
and  cupel  losses  of  gold  and  facilitates  parting.  The  above  is 
an  excellent  process  for  gold  in  mattes,  but  on  account  of  the 
lengthy  scorification,  the  silver  is  apt  to  be  too  low,  and  even 
when  no  silver  is  added,  the  results  on  that  element  are  useful 
only  as  a  rough  check  on  some  other  method.  W.  G.  Perkins  l 
advocated  a  similar  litharge  process  in  1901,  but  reduced  the 
weight  of  sample  with  increase  of  copper. 

1  Trans.  A.  L  M.  E.  31,  931. 


130 


ANALYSIS  OF  COPPER 


2b.  Western  Soda-Niter  Method.  —  Niter  as  a  powerful 
oxidizer  is  preferred  by  many  chemists  in  western  copper  works, 
as  it  lessens  the  quantity  of  litharge.  The  reducing,  power  of 
each  class  of  ore  must  be  known  beforehand.  On  unknown 
ores,  this  may  be  tested  by  a  preliminary  fusion  of  3  grams  of 
ore  with  the  following  charge  :  litharge  50  grams,  sodium  bicar- 
bonate 10  grams.  One  gram  of  niter  oxidizes  4  to  4.7  grams  of 
lead  to  oxide,  and  1  gram  of  flour  will  reduce  10  to  10.5  grams 
of  litharge  to  metallic  lead.  A  good  charge  for  the  final  assay 
is  .5  assay  ton  of  ore,  70  to  100  grams  of  litharge,  15  grams  of 
sodium  bicarbonate,  and  sufficient  niter  to  produce  a  20-gram 
button. 

The  trial  assay  is  avoided  in  regular  daily  tests  of  metallur- 
gical products  of  copper  reduction  works,  because  the  general 
character  of  the  samples  is  known.  A  general  idea  of  the  proper 
composition  of  assay  charges  for  such  products  may  be  obtained 
from  the  table  and  used  as  a  basis  for  experimental  assay  of 
unknown  material. 

The  fluxes  are  given  for  samples  of  1  A.  T.  (29.167  grams). 

CRUCIBLE  METHOD 


Product 

Per 

cent 
Cu. 

Per 

cent 
sulph. 

Lead 
oxide 

Sodi- 
um 
bicarb. 

Powd. 
silica 

Flour 

Potass. 
Nitrate 

Cover 

Ores  — 

grams. 

grams. 

grams. 

grams. 

grams. 

Calcined, 

6-  9 

8-15 

80  to 

50 

5-15 

0-.5 

0-  8 

Thin 

Flue  dust  .  . 

100. 

borax  or 

1"  salt 

Mill  cone,  and 

4^10 

5-40 

150 

35 

10 

0- 

10-40 

1"  salt 

slimes. 

Raw  sulphides 

2-15 

15-30 

150 

35 

10 

0 

10-40 

1*  salt 

Fur.  slags  .... 

.3-2.0 

.5 

80 

50 

.2-4. 

0. 

salt  or 

borax 

Correction  for  Cupels  and  Assay  Slags.  —  This  is  only  made 
when  there  is  an  agreement  between  the  parties  in  a  contract, 
and  is  determined  in  ordinary  cases  on  each  class  of  material 
smelted.  Papers  by  several  authors  have  shown  that  as  the 
size  of  silver  beads  is  increased  the  percentage  loss  of  silver  by 
cupellation  decreases.  The  loss  on  a  20  mg.  bead  may  be  3  to 
5  per  cent  of  the  original  silver,  but  on, a  100  to  150  mg.  bead 
will  be  only  1  to  2  per  cent. 


ASSAYING  FOR  LEAD,  SILVER,  GOLD,  PLATINUM      131 


To  make  a  correction  for  loss  in  firing,  the  leady  portion  of 
cupels  is  ground  to  pass  a  ^Vjneh  screen,  a  pair  of  checks  being 
fused  as  one  sample.  The  silver^  loss  in  a  scorifier  slag  is  usually 
small,  .1  to  .2  ounces  per  ton.  Crucible  and  scorifier  slags  are 
ground  to  pass  a  ^-inch  screen,  fused  in  crucibles  at  a  high 
heat,  and  the  buttons  cupelled,  weighed,  and  parted  for  gold. 


Charge  in  Grams 
(1  inch  salt  cover) 

For  2  cupels 

For  1  A.  ton 
of  slag 

For  2  A.  ton 

of  slag 

Litharge  

30          grams 

20 

40 

Fused  soda  carb  

20-30 

15 

30 

Borax  glass  

30-60 

0 

0 

Cream  tartar  

2-  5 

2 

2 

Temperature  of  Cupellation.  —  Lead  melts  at  about  100°  below 
silver  chloride,  or  at  a  muffle  temperature  of  nearly  326°  C. 
(Rose).  Litharge  freezes  at  840°,  or  when  the  cupel  is  at  907° 
according  to  Bradford.  R.  W.  Lodge  recommends  a  muffle  tem- 
perature of  625  to  800°  C.  Refer  to  papers  on  pyrometry.1 

2c.  Fusion  with  Sodium  Peroxide.  —  Wells  and  Burrows 2 
have  proposed  a  change  in  the  regular  soda-niter  assay,  2b. 
Sodium  peroxide  is  adopted  as  the  oxidizer  of  sulphides,  or 
arsenides,  instead  of  niter,  or  as  a  substitute  for  the  roasting 
process.  Sodium  peroxide  used  with  iron  nails  will  eliminate 
50  per  cent  of  sulphur  from  pure  pyrites.  The  loss  of  gold  or 
silver  is  said  to  be  no  greater  than  with  niter.  This  is  a  promis- 
ing suggestion,  although  the  additional  expense  would  prohibit 
its  use,  probably,  in  custom  work. 

SCORIFICATION 

The  objection  to  the  following  methods,  which  are  yet  speci- 
fied in  some  agreements  in  the  United  States,  is  the  small  quan- 
tity treated  and  the  increased  fire  loss  in  silver  which  repeated 
treatments  involve.  Such  methods  are  better  for  gold  in  me- 
tallic copper  or  matte,  higher  results  being  obtained  for  silver 
in  metals  by  the  combination  of  "wet  and  dry  assaying."3 

3.  Western  Method  for  Matte.  —  The  usual  limits  are,  cop- 
per 30  to  55  per  cent;  silver  30  to  200  ounces  per  ton;  gold  .1 
to  .4  ounce. 

1  F.  P.  Dewey,  /,  Ind.  Eng.  Chem.  6  (1914)  405. 
2  Trans.  A.  I.  M.  E.  34,  387.  3  Note  by  A  M.  Smoot,  Ledoux  &  Co. 


132  ANALYSIS  OF  COPPER 

Scorify  .10  assay  ton  (3  grams)  of  matte  in  a  2.5-inch  (6  cm.) 
scorifier  with  60  to  80  grams  of  lead,  .5  gram  of  borax  glass,  and 
a  little  silica.  This  gives  a  35-gram  button.  Cupel  and  weigh 
the  silver  with  gold,  then  part  as  in  the  crucible  methods,  and 
weigh  the  gold. 

Open  the  scorification  at  a  high  heat  and  continue  at  a 
moderate  temperature.  It  is  often  necessary  to  rescorify  with 
more  lead. 

4.  Silver  in  Clean  Mattes  and  Low-grade  Ores.  —  Although 
the  following  process  is  frequently  specified  for  silver  at  the  port 
of  New  York,  it  is  not  considered  reliable  for  gold,  because  the 
charge  is  too  small  and  there  is  considerable  loss  in  cupellation.1 

Mix  .1  A.  T.  of  sample  with  35  grams  of  test  lead  in  a  3- 
inch  scorifier,  add  35  grams  more  lead  as  a  cover,  and  add  about 
1  gram  of  borax  glass.  Scorify  as  already  directed  and,  if  the 
button  is  soft,  cupel  directly.  If  the  button  is  hard  and  contains 
considerable  copper,  as  will  be  the  case  with  rich  ores  and 
mattes,  make  the  weight  up  to  sixty  grams  by  the  addition  of 
test  lead  and  rescorify  before  cupeling.  At  least  five  assays 
should  be  made  on  each  sample  and  the  beads  united  for  parting. 

5.  Gold  Only,  in  Mattes. 2  —  The  assay  is  similar  to  that  for 
metallic  copper  given  in  the  next  chapter.     Weigh  four  portions, 
each  of  .25  A.  T.,into  four  3-inch  Bartlett  scorifiers  together  with  85 
grams  of  lead  for  each  portion.     Mix  two-thirds  of  the  lead  with 
the  matte  and  use  the  remainder  as  a  cover,  adding  to  each 
assay  two  grams  of  borax  glass.     Open  the  scorifications  very 
hot,  as  in  3,  and  then  continue  at  a  moderate  heat  until  the 
slag   covers   over.     The   lead   buttons   should    weigh    about   30 
grams  each.     Unite  them  two  and  two,  add  a  little  silica,  and 
scorify  again  in  new  scorifiers  to  obtain  15-gram  buttons.     Make 
each  of  these  up  to  90  grams  by  the  addition  of  test  lead,  add  a 
little  silica,  and  scorify  again  to  obtain  30-gram  buttons,  which 
should  be  practically  free  from  copper.     Cupel  at  a  low  heat  and 
part  for  gold  as  described  in  the  nitric  acid  combination  method 
for  metallic  copper,  Chapter  X. 

In  assaying  material  containing  a  large  amount  of  gold  in 
proportion  to  the  silver,  it  is  necessary  to  add  silver  to  the  first 
scorifier  so  that  the  silver  shall  be  six  or  seven  times  as  much  as 
the  gold  present.  The  silver  addition  reduces  slag  and  cupel 

1  Note  by  A.  M.  Smoot.  2  From  A.  M.  Smoot. 


ASSAYING  FOR  LEAD,  SILVER,  GOLD,   PLATINUM      133 

losses  and  facilitates  parting.  This  is  an  excellent  method  for 
gold  in  matte,  but  on  account*  oT  the  repeated  scorifications,  the 
silver  is  apt  to  be  low,  and  even  when  no  silver  is  added,  the 
results  on  that  metal  are  useful  only  as  a  rough  check  on  some 
other  process. 

6.  Combination  Assay  for  Silver  (and  Gold)  in  Mattes. — 
This  method  has  been  used  everywhere  for  mattes  and  copper, 
but  it  gives  low  results  on  gold  owing  to  the  solution  of  a  small 
part  in  the  nitric  acid.1 

For  this  reason,  metallic  copper  is  more  generally  tested 
by  the  "mercury-sulphuric  acid"  method  (Chapter  X),  or 
by  the  bisulphate  method  (8)  which  requires  rather  more  time 
and  attention.  A.  M.  Smoot  prescribes  a  test  which  is  the  most 
satisfactory  for  silver  in  mattes,  especially  when  the  material 
contains  much  bismuth. 

Treat  one  A.  T.  of  sample  in  a  600-c.c.  beaker  with  100  c.c. 
of  water,  add  30  c.c.  of  sulphuric  acid  (d.,  1.84),  a  little  at  a 
time,  if  the  matte  is  high  in  iron;  otherwise  the  evolution  of 
hydrogen  sulphide  may  be  so  violent  as  to  cause  loss.  When 
most  of  the  sulphide  of  iron  has  been  decomposed,  boil  the 
solution  to  eliminate  all  hydrogen  sulphide.  By  this  means  a 
large  part  of  the  sulphur  is  expelled,  and  operations  facilitated. 
To  the  hot  solution,  add  100  c.c.  of  nitric  acid  in  small  portions 
until  the  copper  is  dissolved.  Heat  if  necessary,  dilute  with 
water  to  400  c.c.,  and  filter.  Wash  the  beaker,  wipe  it  carefully 
with  filter  paper,  add  this  to  the  filter,  and  reserve  the  filtrate 
and  washings. 

Scorification.  —  Transfer  filter  and  contents  to  a  litharge- 
glazed  scorifier,  dry  and  burn  the  filter,  best  in  a  closed  oven. 
Add  test  lead  to  the  residue  and  scorify  it  so  as  to  obtain  a 
10-gram  button,  which  is  cleaned  and  reserved.  The  size  of 
the  scorifier  and  quantity  of  test  lead  will  depend  on  the  amount 
of  insoluble  matter. 

To  the  filtrate,  add  sodium  chloride  solution  sufficient  to 
precipitate  all  the  silver,  and  stir  it  until  the  silver  chloride 
agglomerates.  Small  amounts  of  silver  require  the  addition  of 
about  3  c.c.  of  concentrated  lead  acetate  solution  to  form  lead 
sulphate  as  a  collector.  Let  the  silver  settle  —  best  over  night 
—  and  filter  on  double  close  filters.  Wash  the  beaker  and  wipe 
1  J.  Amer.  Chem.  Soc.,  31  (1910),  318  and  1262. 


134  ANALYSIS  OF  COPPER 

it  thoroughly  with  filter  paper,  adding  this  to  the  residue. 
Transfer  the  filter  and  contents  to  a  2.5-inch  litharge-glazed 
scorifier  and  calcine  in  a  closed  oven  until  the  paper  is  charred. 
Remove  to  the  open  air  and  the  remaining  carbon  will  glow 
gently  until  consumed.  Now  add  the  first  button  obtained, 
together  with  enough  test  lead  to  bring  the  total  weight  of  lead 
to  30  grams.  Scorify,  cupel,  weigh,  and  part  as  in  the  nitric 
acid  method  for  copper  (Chapter  X). 

NOTE.  —  Silver  chloride  has  a  melting  point  about  100 
degrees  above  that  of  lead.  The  chloride  should  therefore  be 
reduced  at  a  low  temperature  not  over  the  melting  point  of  lead, 
to  prevent  vaporization.  Loss  may  be  further  prevented  by 
dusting  about  1.5  grams  of  the  powdered  lead  on  the  inside  of 
the  filter  before  charring. 

7.  Combination  Assay  of  Mattes  Containing  Lead.  —  Mattes 
containing  lead  are  not  decomposed  by  sulphuric  acid  sufficiently 
to  make  that  step  worth  while;    moreover,  the  large  amount  of 
lead  sulphate  formed  renders  the  filtration  difficult.     If  the  acid 
method  is  to  be  used,   Smoot  treats  one  assay  ton  of  sample 
with   150  c.c.   of  nitric  acid   (d.,    1.42),   adding  it  slowly  until 
decomposition  is  complete.     Boil,  dilute  to  450  c.c.,  and  proceed 
exactly  as  in  6. 

8.  Special  Assay  for   Gold,   Silver,  and  Platinum  in  Rich 
Ores  and  Mattes.  —  To  avoid  the  loss  of  gold  due  to  nitric  acid, 
and  to  permit  the  exact  separation  of  the  valuable  metals,  the 
author  makes  use  of  sulphuric  acid  only,  adding  a  reagent  to 
facilitate  solution  which  has  no  injurious  effect. 

Although  the  combination  assay,  as  applied  to  ores,  involves 
too  much  manipulation  for  custom  work,  it  has  proved  valuable 
for  the  exact  assay  of  rich  material,  such  as  mattes  and  native 
copper.  The  metals  in  the  insoluble  residue  may  be  collected 
with  very  little  litharge,  avoiding  the  large  slag  loss  of  the 
direct  fire  assay. 

Solution  of  Ores  and  Mattes.  —  Weigh  out  1  assay  ton  (29.167 
grams)  after  grinding  the  sample  to  pass  a  sieve  of  60  meshes  to 
the  linear  inch.  With  native  copper,  prills  or  nuggets  may  have 
to  be  removed  and  separately  tested.  Place  the  material  in  a 
No.  4  casserole.  Then  add  30  grams  of  solid  potassium 


ASSAYING  FOR  LEAD,  SILVER,  GOLD,  PLATINUM       135 

bisulphate,  mix  well,  and  withdraw  the  glass.  With  mattes, 
10  grams  of  sodium  peroxide  fyave.been  occasionally  introduced 
as  an  oxidizing  agent. 

In  either  case,  add  Very  slowly  to  the  covered  casserole  50 
c.c.  of  sulphuric  acid  (d.,  1.84).  Heat  very  slowly  in  the  hood 
with  a  Bunsen  burner,  taking  care  that  the  heat  is  not  high 
enough  to  carry  the  mixture  up  to  the  cover.  About  five 
minutes'  gentle  heat  will  usually  decompose  the  mass  so  that  the 
acid  will  boil  quietly  under  the  cover  and  the  sulphur  will  distill 
and  collect  on  the  under  side  of  the  glass.  Without  moving  the 
cover,  pour  in  30  c.c.  more  acid  and  boil  hard  for  half  an  hour. 
At  the  end  of  this  period,  the  sulphur  should  all  be  boiled  out 
of  the  casserole,  except  possibly  two  or  three  globules.  If 
preferred,  these  may  be  removed  by  longer  boiling  after  washing 
down  with  a  few  drops  of  strong  acid.  Now  dilute  the  cooled 
mass  of  sulphates  with  water  and  heat  to  dissolve  soluble  salts. 
Stir  rapidly  and  add  enough  hydrochloric  acid  to  precipitate  any 
dissolved  silver.  Dilute  to  500  c.c.  and  transfer  to  a  750  c.c. 
beaker.  Allow  to  settle  for  fifteen  minutes  and  filter. 

Place  in  a  small  clay  crucible  the  following  fluxes  :  30  grams 
of  litharge,  30  grams  fused  sodium  carbonate,  10  grams  potassium 
carbonate,  10  grams  borax  glass,  and  .6  gram  of  flour,  or  enough 
to  reduce  a  12-gram  button  of  lead.  Dry  the  filter,  shake  out 
the  contents  carefully  on  top  of  the  mixed  flux,  char  the  filter 
with  an  inverted  burner,  stir  with  a  rod,  cover  with  a  2.5  cm. 
layer  of  salt,  melt,  and  pour  as  usual.  Cupel  the  buttons  at  a 
heat  low  enough  to  feather  properly.  The  slag  loss  is  low,  and 
the  residues  from  three  or  six  solution  assays  may  be  combined 
and  fused  in  a  crucible  as  one  siliceous  ore.  The  F.  F.  Hunt 
Laboratory,  New  York,  uses  a  mixture  of  sodium  sulphite  and 
sulphuric  acid  for  the  same  purpose. 

SEPARATION   OF   SILVER,   GOLD,   AND   PLATINUM 

9.  Direct  Method  of  Separation.  —  At  the  Rambler  Mine, 
the  procedure  is  as  follows:1  Eight  portions  of  one  "assay  ton*" 
each  are  generally  weighed  into  20-gram  crucibles  for  fusion, 
although  the  quantity  of  sample  depends  on  the  richness  of  the 
product.  If  much  copper  is  present,  the  buttons  are  rescorified 
1  A.  C.  Dart,  Met.  and  Chem.  Eng.  9,  75;  10,  219. 


136  ANALYSIS  OF  COPPER 

until  soft  and  then  cupeled.     Thus   far  the   preceding  method 
could  be  employed  to  advantage. 

When  the  total  precious  metals  have  been  weighed,  they  are 
combined  in  two  check  lots,  representing  four  assay  tons  each, 
and  are  then  cupeled  again  with  ten  times  their  weight  of  pure 
silver.  The  resulting  buttons  are  parted  separately  with  12  per 
cent  nitric  acid,  and  finally  in  strong  nitric  acid  in  test  tubes 
placed  in  boiling  water.  Silver,  palladium,  and  platinum  are 
thus  dissolved  and  gold  remains.  The  residue  is  now  washed  in 
the  usual  way,  and  the  gold  ignited  and  weighed.  The  nitric 
acid  solution  from  the  preceding  step  is  kept  as  small  in  volume 
as  possible. 

The  silver  is  separated  by  precipitation  as  chloride,  which  is 
filtered  off  and  washed  free  from  acid. 

Platinum  and  palladium  are  obtained  from  the  filtrate,  which 
is  evaporated  to  dryness,  and  redissolved  in  a  few  drops  of 
hydrochloric  acid  and  10  c.c.  of  hot  water.  This  solution  is 
allowed  to  stand  for  half  an  hour,  and  if  silver  chloride  separates, 
it  is  again  filtered  and  washed,  the  precipitate  being  combined 
with  the  first  obtained.  The  filtrate  is  now  made  ammoniacal, 
then  acidified  with  formic  acid  and  boiled.  This  will  precipitate 
metallic  platinum  and  palladium,  which  are  filtered,  or  washed 
by  decantation,  ignited,  and  weighed. 

Separation  of  Platinum  and  Palladium.  —  The  weighed  metals 
are  converted  into  chlorides  by  dissolving  in  aqua-regia,  evaporat- 
ing to  dryness,  and  taking  up  with  a  few  drops  of  hydrochloric 
acid  and  50  c.c.  of  hot  water.  This  solution  is  saturated  with 
pure  crystallized  ammonium  chloride;  10  c.c.  of  alcohol  are 
added,  and  the  whole  allowed  to  stand  not  less  than  twenty-four 
hours.  The  ammonium  platinic  chloride  is  then  filtered,  washed 
with  a  saturated  solution  of  ammonium  chloride,  and  ignited 
very  slowly  to  prevent  loss  of  metal.  The  resulting  platinum  is 
weighed  and  the  gold  having  been  already  directly  weighed,  the 
silver  is  obtained  by  difference.  If  a  trace  of  platinum  is  sought, 
reduce  the  volume.  Palladium,  if  present,  is  determined  by  the 
difference  between  the  combined  weight  of  palladium  +  platinum, 
and  the  platinum  precipitated  by  ammonium  chloride. 

It  is  generally  considered  that  more  than  one  fusion  of  gold 
with  ten  parts  of  silver  is  required  to  remove  every  trace  of 
platinum.  Unless  the  platinum  is  considerable,  the  old  way  of 


ASSAYING  FOR  LEAD,  SILVER,   GOLD,   PLATINUM      137 

parting  with  boiling  sulphuric  acid  —  taking  the  weight  of  gold 
with  platinum,  and  then  remelting  with  excess  of  silver  and 
parting  with  nitric  acid  for  gold* — gives  uncertain  figures  on 
the  platinum  calculated  by  difference,  unless  the  gold  is  also 
very  small  in  amount.1 

10.  Indirect  Method.2  —  All  the  platinum  (after  parting  the 
silver  with  nitric  acid)  may  be  removed  from  solution  by  a 
partial  precipitation.  The  gold  is  first  removed  by  decantation, 
or  better,  by  filtration.  The  essential  details  are  as  follows  : 
Small  amounts  of  platinum  will  readily  dissolve  in  nitric  acid 
with  the  silver.  If  now  a  limited  amount  of  hydrogen  sulphide 
water  be  added  to  the  solution  from  parting,  any  platinum 
present  will  be  precipitated  as  sulphide,  along  with  some  silver 
sulphide.  After  filtering  and  slightly  washing,  the  moist  filter  is 
transferred  to  a  small  porcelain  crucible,  dried  at  a  low  heat, 
and  burned  off  by  gentle  ignition.  This  transforms  the  platinum 
to  a  metallic  sponge,  which  is  wrapped  in  a  small  piece  of  lead 
foil  and  cupeled.  The  resulting  bead  is  then  parted  in  strong 
sulphuric  acid,  when  the  platinum  will  be  left  as  a  dark  residue, 
generally  in  spongy  form  even  when  minute  in  quantity.  This 
sponge,  after  reboiling  in  fresh  acid,  if  necessary,  is  suitably 
washed  by  decantation,  annealed,  and  weighed.  The  platinum 
may  be  dissolved  in  a  drop  or  two  of  aqua-regia  and  gently 
evaporated.  The  solution  obtained  may  be  tested  with  potas- 
sium iodide,  or  a  few  small  crystals  of  ammonium  chloride  may 
be  added  when  the  characteristic  precipitate  will  show  itself. 
This  may  be  filtered  off  and  gently  ignited.  If  considerable, 
the  platinum  may  be  determined  by  the  double-chloride  method. 
Any  decided  difference  shown  would  indicate  the  presence  of 
other  members  of  the  platinum  group,  for  which  a  direct  test 
could  then  be  made. 

NOTE  (on  hydrogen  sulphide  treatment) .  —  A  very  dilute  solu- 
tion should  be  used,  diluting  the  saturated  solution  with  about 
15  parts  of  water,  and  using  15  c.c.  of  the  diluted  reagent  for  an 
ore,  or  30  c.c.  for  a  bullion.  The  reagent  should  be  added  very 
slowly  to  the  silver  nitrate  solution  with  constant  stirring.  The 
solution  should  darken,  but  not  visibly  precipitate.  The  solution 

1  Second  Method  —  Met.  Chem.  Eng.  12  (1914)  481. 

2  Method  of  F.  P.  Dewey.    See  method  of  Smoot,  Eng.  &  Min.  J.  99  (1915) 
700. 


138  ANALYSIS  OF  COPPER 

should  be  stirred  occasionally  for  two  hours,  when  flocks  should 
appear,  which  may  be  filtered  off  in  3  to  4  hours,  although  it  is 
better  to  settle  over  night.  , 

If  only  minute  amounts  of  platinum  are  present,  it  is  still 
necessary  to  add  sufficient  hydrogen  sulphide  to  give  a  silver 
bead  large  enough  to  handle  comfortably.  It  may  happen  that 
the  final  metal  shows  the  yellow  color  of  gold,  due  to  the  fact 
that  exceedingly  fine  float-gold  passed  over  in  decanting.  In 
such  a  case  the  metal  must  be  realloyed  with  silver  and  the 
treatment  repeated.  When  the  proportion  of  gold  to  the  silver 
in  the  metal  being  parted  is  so  small  that  the  gold  separates  in. 
a  finely  divided  state,  it  will  often  save  trouble  to  filter  the 
silver  nitrate  solution,  before  adding  hydrogen  sulphide. 

NOTES.  —  Coin  silver  may  also  be  tested  by  this  method, 
taking  about  100  grams,  evaporating  the  nitric  acid  solution 
nearly  to  dry  ness,  and  treating  with  5  c.c.  of  strong  hydrogen 
sulphide,  diluted  to  50  c.c.  Much  platinum,  alloyed  with  silver, 
is  not  entirely  soluble  in  nitric  acid.  Hence  the  operation  of 
alloying  the  gold  with  silver  and  parting  must  be  repeated  a 
second,  or  even  a  third  time,  when  such  material  is  assayed. 

For  the  separation  of  the  rarer  elements  of  the  platinum 
group,  occurring  in  minerals,  refer  to  the  report  of  the  inter- 
national committee  on  analyses  to  the  Eighth  International 
Congress  of  Applied  Chemistry,  pp.  1-24. 

THE  FIRE   ASSAY   OF   NATIVE     COPPER 

11.  Lake  Superior  Method.  —  The  refineries  of  northern 
Michigan  employ  as  an  alternative  or  substitute  for  the  electro- 
lytic method,  a  short  direct  fire  assay,  which  is  only  successful 
in  the  entire  absence  of  sulphur  and  sulphates  from  the  ores  or 
chemicals.1 

The  description  of  this  process  is  condensed,  as  it  is  only 
of  local  interest.  The  materials  subjected  to  fire  assay  are  :  — 
(1)  Rich  " cover"  work,  or  coarse  heading  from  the  mortars, 
about  90  per  cent  copper;  (2)  finer  mill  concentrates  from  jigs, 
containing  65  to  90  per  cent  copper;  (3)  slime  concentrates, 
from  revolving  or  shaking  tables,  20  to  30  per  cent  copper.  The 
ideal  would  be  attained  if  the  copper  could  all  be  reduced  into  a 
1  J.  Am.  Chem.  Soc.  24;  Eng.  and  Min.  J.  1895,  369. 


ASSAYING  FOR  LEAD,   SILVER,   GOLD,   PLATINUM      139 

button  in  one  short  fusion,  without  a  simultaneous  reduction  of 
some  iron  into  the  button.  As  most  of  the  arsenic  enters  the  refined 
metal,  it  is  reduced  and  weighed  with  the  copper  as  far  as 
possible.  Concentrates  (over  40  per  cent  copper)  are  so  fluxed 
and  fired  that  the  loss  of  copper  in  the  slag  is  limited  to  about 
.25  per  cent  of  the  mineral  weighed,  and  is  balanced  by  iron 
reduced  into  the  copper  button  equivalent  to  .25  per  cent  of  the 
original  sample.  On  such  material  it  is  possible  for  the  assayer, 
after  two  months'  practice,  to  tell  by  inspection  the  purity  of 
the  button  within  a  limit  of  .1  per  cent,  either  way.  The 
button  should  have  a  bright  color,  and  set  with  a  cavity  on  the 
upper  surface  when  cooled  under  the  slag  without  pouring.  The 
surface  should  be  striated. 

Low  grades  (below  40  per  cent  copper)  cannot  be  visuall}7" 
estimated  as  closely,  but  a  button  entirely  free  from  iron  can  be 
distinguished  from  one  carrying  enough  iron  to  affect  the  assay 
result  on  1000-grain  samples  more  than  .1  per  cent.  Such  small 
buttons  show  no  cavity  on  the  upper  surface,  but  should  be 
bright  in  color  and  soft  under  the  hammer.  Accordingly,  low- 
grade  concentrates  are  fired  with  less  reducer  to  obtain  a  pure 
button,  and  the  copper  lost  in  the  slag  (.35  to  .5  per  cent)  is 
quickly  estimated  with  sufficient  accuracy  by  making  a  rough 
calculation  of  the  total  weight  of  slag  produced,  crushing  a 
sample  of  it,  and  estimating  the  copper  by  the  colorimetric  test, 
described  in  Chapter  IV.  The  total  weight  of  copper  slagged  is 
calculated  and  added  to  the  weight  of  the  button.  Check 
assays  on  very  heavy  coarse  material  should  agree  within  about 
.5  per  cent,  on  finer  grades  within  .2  to  .4  per  cent,  and  on  slimes 
within  .2  per  cent,  including  the  errors  of  sampling.  From 
month  to  month  the  fire  assay  results  check  quite  closely  the 
weighed  output  of  the  reverberatory  furnaces,  adding  the  loss 
in  slag  from  remelting  cupolas. 

The  electrolytic  assay,  applied  to  an  equally  large  sample  of 
at  least  60  grams  (1000  grains),  may  furnish  accurate  results,  but 
it  does  not  include  the  arsenic  present  in  some  Lake  copper. 
For  electrolysis,  the  sample  would  be  dissolved  in  dilute  nitric 
acid,  diluted  to  one  liter,  and  100  c.c.  of  the  mixed  solution 
withdrawn  for  electrolysis.  If  a  residue  of  coarse  gravel  remains 
undissolved,  it  should  be  dried,  ground,  and  extracted  again. 

The  fire  assay  furnishes  results  in  less  time,  which  are  well 


140  ANALYSIS  OF  COPPER 

within  the  limits  of  error  in  daily  sampling.  Any  pimples  or 
purple  films  on  an  assay  button  indicate  sulphur,  or  intrusion 
of  fragments  of  coal.  The  color  of  the  slag  should  vary  from 
dark  brown  to  black  with  the  lower  grades. 

Furnace.  —  Assayers  employ  a  rectangular  pot  furnace,  as 
illustrated  in  Chapter  I,  heated  by  coke  and  air  blast  from  the 
smallest  commercial  size  of  power  blower  through  a  2.5-inch 
pipe. 

Two  rows  of  fire  brick  (of  2.5  x  2.5  inches  cross-section) 
are  placed  across  the  grate  and  the  fuel  is  kept  at  least 
two  inches  above  the  bricks.  More  fuel  is  filled  in  around  the 
crucibles  after  they  have  been  placed  on  the  cleaned  bricks. 
Different  grades  from  lodes  of  different  formation  and  tenor  in 
copper  require  radical  changes  in  the  fluxes,  especially  in  the 
reducing  agent.  As  the  heat  must  be  very  high,  the  crucible 
lining  affects  the  slag.  A  basic  Denver  clay  crucible,  when 
covered,  requires  more  flux  but  less  reducer  than  a  more  open- 
shaped  sand  crucible. 

Fluxes.  —  The  chemicals  must  be  pure.  Sodium  bicarbonate 
is  first  fused  in  a  large  iron  ladle  without  handle,  poured  into  a 
smooth  iron  dish  to  cool,  and  pulverized  through  a  20-mesh 
sieve.  Refined  borax  is  melted  in  a  Dixon  graphite  crucible, 
poured  into  an  iron  dish;  and  pulverized.  Powdered  silica  and 
hematite  are  employed,  occasionally,  as  a  corrective,  so  that  the 
assay  slag  may  contain  the  average  amount  of  ferrous  silicate 
which  experience  shows  to  be  the  best. 

Weighing.  —  The  moist  concentrates  from  the  bins  (represent- 
ing the  daily  tonnage  of  each  grade  of  mineral)  are  successively 
placed  on  a  15-by-19  inch  vulcanite  photographic  tray  which 
serves  as  a  sampling  board.  The  tray  (one  side  of  which  is  cut 
out)  is  slightly  moistened  with  a  damp  cloth,  the  sample  is 
coned  up,  flattened  to  a  layer  about  an  inch  thick,  and  a  dip 
sample  of  1000  Troy  grains  (64.8  grams)  taken  at  nine  points 
by  cutting  vertical  slices  with  a  10-inch  steel  spatula.  This 
sample  is  then  mixed  on  a  glazed  paper  with  the  weighed  fluxes 
and  placed  in  the  marked  crucibles.  Duplicates  are  taken  of 
single  samples,  as  also  a  moisture  sample  of  the  same  amount, 
which  is  placed  in  a  small  tin  cup  and  dried  on  the  steam  plate. 
From  these  data,  the  percentages  of  copper  may  be  figured  to  the 
dry  weights  of  mineral.  Mineral  containing  70  to  95  per  cent 


ASSAYING  FOR.  LEAD,   SILVER,   GOLD,   PLATINUM      141 


copper  makes  so  little  slag  of  itself  that  there  would  not  be 
enough  to  cover  the  button  and  keep  it  deoxidized  while  cooling. 
Accordingly,  a  large  stock  of,  old  assay  slag  is  accumulated, 
assayed  for  copper,  and  a  known  quantity  added  to  each  charge 
of  rich  material  to  act  as  a  cover  and  regulator.  If  this  assay 
slag  is  of  average  copper  tenor,  no  account  is  taken  of  the  copper, 
as  it  would  not  add  to,  or  lessen,  the  weight  of  the  button. 

The  mineral  and  fluxes  are  mixed  on  the  paper,  then  brushed 
into  the  crucibles,  and  a  3  mm.  layer  of  cream  of  tartar  dusted 
over  each  charge.  The  crucibles  are  closed  with  covers  made 
from  a  mixture  of  fire  clay  and  ground  brick.  The  coke  is  filled 
in  around  the  crucibles,  and  the  blast  started.  Thousand-grain 
assays  should  be  melted  down  to  clear  fusion  in  twelve  to  thirteen 
minutes,  then  withdrawn,  and  uncovered  while  cooling. 

The  very  coarse  " heading"  can  only  be  tested  with  sufficient 
accuracy  by  taking  several  pounds  for  the  original  sample, 

FLUXES  FOR  MILL  CONCENTRATES  OF  NATIVE  COPPER 


Sample 

Grade 

Per 
cent 
copper 

Cream 

tartar 

Fused 
soda 
carb. 

Borax 
glass 

Assay 
slag 

Iron 
oxide 

Fine 
sand 

27000  to 
35000. 
2000. 

Heading 
Coarse  jig 

90-92 
95-90 

iso 

1000 
300 

400 
150 

1000 
300 





1000. 

Fine  No.  1-2 

65-75 

350 

150 

50 

250 

1000. 
1000. 

Table  slimes, 
Conglomer- 
ate 
Amygd.,  low 
Fe. 

20-25 
20-40 

300 
250 

200 
200 

200 
200 

50-150 

0-100 

Cover.  —  Cream  tartar,  in  all  cases. 

drying  it  in  a  milk  pan  to  obtain  the  moisture  per  cent,  then 
dividing  the  sample  in  halves  and  melting  3  to  5  pounds  in 
Denver  K  or  L  Battersea  crucibles.  To  avoid  softening  and 
cracking  the  crucibles  with  such  a  heavy  charge,  the  blast  should 
not  be  used.  The  fusion  may  be  completed  with  the  natural 
draft  in  about  one  hour.  All  melts  should  be  withdrawn  from 
the  furnace  just  as  soon  as  they  reach  quiet  fusion,  in  order  to 
avoid  undue  reduction  of  iron  into  the  button.  The  crucibles 
should  not  be  jarred  \vhilo  r^1''^. 


142  ANALYSIS  OF  COPPER 

The  total  weight  of  slag  produced  from  70  per  cent  mineral 
is  about  600  grains,  and  from  table  (slime)  concentrates,  about 
1200  grains,  when  a  1000-grain  sample  is  assayed.  The  propor- 
tions of  fluxes  for  different  grades  are  ascertained  by  experiment. 
The  following  table  is  appended  as  a  basis  or  starting  point, 
from  which  the  assayer  can  produce  other  similar  combinations. 
All  weights  are  given  in  grains  Troy.  One  gram  =  15.432  grains. 


PART   II 
CHAPTER  IX 

WORK  OF  THE  ELECTROLYTIC  REFINERY 
SECTION  1.    ASSAY  OF  GOLD  AND  SILVER  BULLION 

1.  Dore,    or    Unparted    Base  Bullion   (F.    D.    Greenwood). 
Cupellation  in  Presence  of  Gold,  Silver,  Copper,  and  Lead.  —  The 
sampling  has  been  described  on  the  last  page  of   Chapter  II. 
One  gram  of  Dore  is  weighed  into  a  piece  of  lead  foil  of  about 
six  grams'  weight,  rolled  into  a  cornucopia,  and  cupeled.     The 
cupel  should  be  " feathered"  nicely;    cupel  to  be  made  of  bone- 
ash,  passing  through  a  sieve  of  60  meshes  to  the  linear  inch 
(24  per  cm.),  and  to  be  of  medium  hardness. 

Weigh  the  tube  and  place  same  in  test  tube,  add  10  c.c. 
nitric  acid  (1  part  HNO3  (d.,  1.42)  to  5  parts  water).  Place 
test  tube  in  beaker  of  water  and  warm  until  action  ceases,  then 
bring  water  to  a  boil.  Pour  off  acid  and  wash  with  distilled 
water,  then  add  about  5  c.c.  nitric  acid  (d.,  1.42),  and  place  test 
tube  in  a  beaker  of  water  and  boil  for  one  half  hour.  Pour  off 
acid  and  wash  three  times  with  distilled  water.  Place  the  gold 
in  a  porcelain  crucible,  dry,  anneal,  and  weigh. 

A  proof  must  be  run  and  treated  exactly  as  the  Dore  is  in 
each  stage,  and  a  surcharge  added  or  subtracted,  as  the  proof 
loses  or  gains.  A  preliminary  assay  is  made  of  the  Dore*,  and 
the  proof  made  up  accordingly.  An  assay  consists  of  three  Dore 
weighings  and  two  proofs,  cupeled  in  the  following  order,  and 
at  the  same  time:  1st,  Dore;  2d,  proof;  3d,  Dore;  4th,  proof; 
5th,  Dore. 

2.  For  Dore  containing  Antimony.  —  The  gram   portion  is 
weighed  into  a  2J-inch  (6.3  cm.)  scorifier  with  30  grams  of  test 
lead.     The  proofs  are  made   up   according  to  the  preliminary 
assay.     All  are  scorified  in  the  same  muffle  at  the  same  time. 
Pour  and  hammer  the  lead  buttons  into  a  cube.     Should  the 
weight  of  these  lead  buttons    vary    over  a  gram,  make  up  to 


144  ANALYSIS  OF  COPPER 

equal  weights  with  sheet  test-lead,  cupel,  and  treat  exactly  as  in 
No.  1. 

3.v  For  Dore  containing  Bismuth,  Selenium,  and  Tellurium.  — 
Three  1-gram  portions  are  weighed  out  into  a  2.5-inch  (6.3  cm.) 
scorifier  with  40  grams  of  test  lead,  scorified,  and  the  lead  buttons 
flattened  out  into  a  sheet  about  3  inches  square.  This  sheet  of 
lead  is  dissolved  in  about  200  c.c.  of  dilute  nitric  acid  (1:3) 
and  boiled  to  expel  red  fumes,  diluted  to  400  c.c.,  and  filtered 
through  three  15  cm.  filters  folded  as  one,  washing  the  precipitate 
only  once.  Place  the  three  filter  papers  in  a  2.5-inch  lead  lined 
scorifier,  dry  in  an  oven,  burn,  then  cover  with  30  grams  of  test 
lead,  and  scorify.  Open  the  scorification  at  a  rather  high  heat, 
continuing  with  a  gradually  falling  temperature.  When  the 
scorifiers  have  entirely  closed  over,  close  the  muffle  door,  raise 
the  heat,  and  pour;  then  treat  exactly  as  in  method  2.  If  the 
silver  fineness  of  the  Dore  is  not  three  or  more  times  greater 
than  the  gold  fineness,  another  set  of  assays  must  be  run,  with 
the  addition  of  proof  silver  at  the  weighing  out  of  the  Dore. 

MINT  ASSAY  OF  PURE  UNPARTED  BARS,  OR  FINE  GOLD  AND  SILVER 

4.  Assay  for  Gold.  —  In  all  the  electrolytic  refineries  of  the 
United  States  and  Europe  the  pure  material  is  sampled  and 
assayed  practically  in  the  manner  prescribed  in  the  respective 
Mints  or  Government  Assay  Offices  which  purchase  the  bullion. 
The  assay  for  fine  gold  at  the  Raritan  works,  for  example,  varies 
only  in  the  amount  of  sample  used,  duplicate  portions  of  250 
mg.  each  being  weighed  out  instead  of  500  mg.,  the  amount 
taken  at  the  mints.  Dr.  Edward  Keller's  valuable  suggestion  on 
the  application  of  copper  plate  sampling  methods  to  bullion  is 
noted  in  the  last  section  and  page  of  Chapter  II. 

A  proof  of  the  solubility  of  gold  in  nitric  acid  and  a  discus- 
sion of  the  conditions  affecting  the  accuracy  of  the  gold  assay 
were  presented  in  two  papers  by  F.  P.  Dewey.1  The  account  of 
the  Mint  method  has  been  written  up  from  these  papers,  from  the 
method  of  J.  B.  Eckfelt  in  the  Mint  report  of  1896,  and  from 
the  report  of  Whitehead  &  Ulke,2  including  a  few  personal  notes. 

Assay.  —  The  Mint  sample  is  usually  taken  as  a  triangular 
chip  from  top  and  bottom  of  diagonally  opposite  corners  of  a 

1  J.  Am.  Chem.  Soc.  31  (1910),  318.  Trans.  A.  I.  M.  E.  40,  780  (1909). 

2  Eng.  and  Min.  Jour.  1898,  189. 


WORK  OF   THE  ELECTROLYTIC  REFINERY  145 

bar  (see  Chapter  II).  The  assay  balance  should  be  sensitive  to 
.01  mg.,  and  be  provided  with  reading  lenses.  The  chips  are 
flattened,  by  hammer  or  hydraulic  press,  or  rolled  to  a  ribbon, 
marked  by  stamp  wittr  a  lot  number  in  such  a  way  that  the  top 
can  be  distinguished  from  the  bottom,  and  the  approximate 
fineness  determined  by  preliminary  assay,  or  by  comparison  on 
the  " touch  stone"  with  " needles"  of  gold  of  different  degrees  of 
fineness.  Practice  enables  an  expert  to  judge  within  a  few 
thousandths. 

To  the  accurately  weighed  gold  there  is  added  sufficient  fine 
silver,  also  accurately  weighed,  to  make  about  twice  (or  three 
times,  according  to  another  system  now  less  used)  the  estimated 
amount  of  gold  in  the  alloy.  (It  is  customary  to  make  the 
preliminary  assay  when  the  gold  contains  much  base  metal.) 
Extreme  care  is  necessary  that  the  amount  of  silver  added  varies 
as  little  as  possible  from  the  above  proportion,  as  in  any  marked 
divergence  the  result  would  be  liable  to  inaccuracy.  The  fact 
must  be  emphasized  that  good  results  can  be  obtained  with 
either  proportion  of  silver,  because  the  whole  process  is  com- 
parative, the  "proofs"  being  made  up  to  agree  with  each  set  of 
samples  in  composition,  and  carried  through  under  exactly  the 
same  conditions.  If  more  silver  is  used  than  (2:1),  the  first 
acid  in  parting  is  made  weaker  to  avoid  too  violent  an  action. 

The  Mints  now  take  for  assay  500  mg.  of  gold,  and  besides 
the  silver,  add  about  50  mg.  of  pure  copper  if  there  is  none 
present,  as  it  assists  the  cupellation,  making  the  resulting  button 
tough  on  the  edges  and  the  final  "cornet"  smooth.  One  or  two 
proofs  are  included  with  each  set  of  assays  of  the  same  kind,  to 
detect  inaccuracies  and  particularly  to  afford  the  correction  for 
"surcharge"  to  be  applied  to  the  final  results.  The  assays  and 
proofs  having  each  been  inclosed  in  five  grams  of  lead  foil,  the 
assays  are  ready  for  the  furnace.  Some  assay ers  introduce  the 
leads  to  the  hot  cupels  by  a  cupel  charger,  such  as  that  of 
Keller,  which  holds  forty-eight.  T.  K.  Rose,  Chemist  of  the 
English  Mint,1  uses  a  similar  apparatus  made  by  Westwood, 
taking  seventy-two  at  one  time,  and  the  cupels  are  arranged  on 
a  plumbago  tray  which  is  lifted  out  of  the  muffle  by  an  iron  peel, 
the  proofs  being  evenly  distributed  through  the  charge.  The 

1  Thirty-fifth  Ann.  Rep.  Eng.  Mint,  1904,  70.  Eng.  and  Min.  Jour.  80 
(1905),  492. 


146  ANALYSIS  OF  COPPER 

English  Mint  considers  it  an  improvement  to  close  the  space  at 
the  back  of  muffle  with  fire  clay  to  prevent  over-heating;  and 
instead,  make  an  opening  in  the  top,  maintaining  a  separate 
draft  for  the  muffle. 

Cupellation.  —  After  charging  the  muffle,  the  door  is  closed 
until  the  leads  are  melted  and  the  buttons  commence  to  "drive/7 
when  the  door  is  opened  until  a  few  minutes  before  the  assays 
are  finished.  When  agitation  ceases  and  the  metal  presents  a 
bright  surface,  the  cupels  are  allowed  to  cool  gradually,  and  the 
button  of  pure  gold  and  silver  detached.  The  exact  temperature 
and  time  are  a  jnatter  of  experience.  The  button  is  brushed 
clean  and  weighed,  then  hammered,  annealed,  and  rolled  in 
small  special  rolls  to  a  thin  strip  to  furnish  a  larger  surface  for 
the  action  of  the  acid.  The  strips  are  then  coiled  around  a 
pencil,  or  rod,  with  the  stamped  end  outside. 

Parting.  —  If  a  few  assays  are  made  at  a  time,  as  in  some 
refineries,  the  cornets  are  parted  in  crucibles,  or  test  tubes.  The 
Mints  use  platinum  basins  of  boiling  nitric  acid,  into  which  are 
dipped  platinum  baskets,  holding  16  small  cups  of  platinum  for 
the  cornets.  The  first  basin  contains  nitric  acid  about  (1  :  1), 
or  22°  Beaume  if  three  parts  of  silver  have  been  used.  If  but 
two  parts  to  one  of  gold  (a  former  method)  are  taken,  the 
acid  is  strengthened  to  32°  Be.  According  to  F.  P.  Dewey 
(J.  Am.  Chem.  Soc.  1910,  320),  the  cornets  are  now  boiled 
twice  in  the  weaker  acid  for  ten  minutes  each  time,  and 
then  in  the  stronger  (3  :  2)  acid  for  ten  minutes.  The  cornets 
are  then  well  washed  with  pure  water,  transferred  to  small  clay 
annealing  cups,  or  dried  in  the  platinum  cups,  and  annealed  and 
weighed.  The  fineness  of  the  gold  is  expressed  in  thousandths. 
By  the  deviation  of  the  proof,  the  proper  correction  is  made 
upon  the  regular  assays,  which  went  through  the  same  furnace 
charge  and  were  of  the  same  composition. 

Platinum.  —  In  an  assay  of  gold  containing  platinum,  the  sil- 
ver must  be  determined  by  a  wet  method,  forming  a  partible 
alloy  by  fusion  with  a  diluent  metal  such  as  cadmium.  The 
parting  operation  does  not  entirely  remove  the  silver,  at  least, 
not  unless  more  than  three  parts  of  silver  were  present  to  one  of 
gold.  The  " surcharge"  of  silver,  or,  exactly  speaking,  the  dif- 
ference between  the  firing  loss,  and  gain  due  to  retained  silver 
is  very  minute,  and  varies  from  two  to  seven  or  eight  ten- 


WORK  OF  THE  ELECTROLYTIC  REFINERY  147 

thousandths.  According  to  Whitehead,  duplicates  should  agree 
within  .2  or  .3  of  a  part  except  in  the  case  of  very  base 
bullion. 

In  assaying  fine  (or  nearly  fine)  gold,  the  proof  is  weighed  to 
1000  parts  of  test  gold;  but  in  testing  ingots  for  coinage,  etc., 
a  proof  of  900  parts  is  used,  and  in  lower  grades  a  synthetic 
proof  is  made  up  to  correspond,  as  already  explained.  Dupli- 
cate assays  serve  also  to  show  if  the  gold  bars  are  of  uniform 
fineness  throughout.  If  the  assays  show  undue  variation,  the 
mass  from  which  the  sample  was  taken  is  remelted  and  stirred 
(after  Mint  methods),  then  cast  and  assayed  in  duplicate  as 
before.  It  is  often  expedient,  with  low-grade  gold,  to  add 
sufficient  fine  gold  (as  in  Dbre  methods),  in  order  that  the  assay 
may  contain  900  parts  of  gold  in  1000.  In  this  way  the 
exact  fineness  of  the  alloy  is  ascertained,  otherwise  a  slight 
allowance  would  have  to  be  made  for  the  cupel  loss,  which  will 
happen  when  a  large  proportion  of  alloy  is  present.  When  the 
weight  of  cornet  is  obtained,  the  weight  of  fine  gold  which  was 
added,  must  be  deducted,  the  difference  being  the  fineness  of 
the  original  alloy. 

Sometimes  the  ordinary  amount  of  lead  is  insufficient  to 
completely  eliminate  all  the  base  metals,  or  the  cupel  may  not 
be  able  to  absorb  all  the  lead  which  such  an  assay  would  re- 
quire. In  such  cases  it  is  accordingly  customary  to  weigh  the 
assay  at  one-half  the  usual  weight,  adding  fine  gold  sufficient 
to  render  the  mixture  900  fine,  and  then  adding  enough  silver 
to  secure  the  right  proportion  of  the  latter  to  the  gold.  Some 
chemists  use  a  system  of  "gold  weights"  in  which  1000  parts 
equals  .5  gram. 

5.  Preparation  of  Pure  Gold.  —  Refineries  may  obtain  their 
proof  gold  directly  from  the  Governments.  Such  metal  can  be 
prepared  by  the  method  of  McCaughey  1  and  Eckfeldt.  Proof 
gold  at  the  Philadelphia  Mint  was  made  from  electrolytic  of 
999  fineness.  The  latter  was  dissolved  in  aqua-regia  and  allowed 
to  stand  for  two  weeks.  The  solution  was  decanted  from  any 
silver  chloride,  and  potassium  chloride  and  alcohol  added  to 
precipitate  any  platinum.  After  standing  two  weeks,  the 
solution  was  decanted  and  precipitated  with  sulphur  dioxide. 
The  gold  was  redissolved,  the  above  steps  repeated,  and  the  final 
1  J.  Am.  Chem.  Soc.  31,  1262. 


148  ANALYSIS  OF  COPPER 

precipitation  made  with  oxalic  acid.  The  separated  gold  was 
melted  in  Beaufay  crucibles  under  borax,  and  rolled  into  rib- 
bons .009  inch  thick.  From  this  ribbon,  little  pieces  were  taken 
and  washed  with  alcohol.  F.  P.  Dewey  quotes  the  same  method. 

FINENESS   OF   SILVER  BULLION 

Limitation  of  Methods.  —  The  cupellation  method,  used  for 
gold,  gives  such  uncertain  results  for  silver  in  high-grade  bullion 
that  it  is  now  used  in  a  subsidiary  way  for  approximate  results 
(Eckfeldt).  The  "wet"  or  humid  assay  of  Gay  Lussac,  with 
proper  care  and  attention,  may  be  regarded  as  a  perfect  process, 
if  performed  by  an  expert  operator.  Some  refineries  employ  a 
combination  method  which  is  more  convenient. 

6.  The  Humid  Silver  Assay  (F.  P.  Dewey).1  — 1115  mg.  of 
standard  metal  (generally  about  900  fine  to  1000  parts)  is 
weighed  and  transferred  to  a  glass-stoppered  bottle,  the  metal 
dissolved  in  nitric  acid,  and  100  c.c.  of  a  standard  solution  of 
sodium  chloride  run  in.  The  bottle  is  then  vigorously  shaken 
and  a  measured  portion  of  a  decimal  salt  solution  added,  and 
again  shaken,  if  necessary.  These  operations  are  repeated  until 
the  silver  is  precipitated.  If  standard  "(900  fine)  silver  is  to 
be  tested,  1115  mg.  should  carry  1003.5  mg.  of  silver,  a  con- 
venient figure.  The  variation  of  such  metal  in  actual  silver 
present  above  or  below  1003.5  mg.  is  not  excessive.  For  testing 
the  standard  salt  solution,  1004  mg.  of  proof  silver  is  weighed 
and  single  weights  are  used  of  1115  and  1004  mg. 

(In  some  copper  refineries  the  metal  to  be  valued  is  the  fine 
bullion  produced  by  parting  and  refining  the  Dore  and  with  such 
pure  metal  about  1004  mg.  would  be  taken.) 

The  bottles  should  be  of  perfectly  white  glass,  carefully  made 
and  well  annealed;  8  ounces  (250  c.c.)  is  a  convenient  size  often 
used;  the  bottles  are  most  conveniently  handled  in  a  circular 
frame  or  basket  holding  ten.  For  dissolving  the  silver,  both  the 
amount  and  strength  of  nitric  acid  may  vary  considerably  with- 
out apparent  effect  upon  the  accuracy  of  the  results,  8  c.c.  at 
1.30  sp.  gr.  to  25  c.c.  at  1.20  sp.  gr.  being  allowable.  Some 
operators  heat  the  bottle  to  remove  nitrous  fumes,  others  do 
not.  The  standard  salt  solution  is  designed  to  have  100  c.c. 
precipitate  exactly  1  gram  or  1000  mg.  of  silver,  but  it  seldom 
1  Bull.  A.  I.  M.  E.  76  (1913),  587. 


WORK  OF  THE  ELECTROLYTIC  REFINERY  149 

" shows"  this  exact  strength.  The  word  " shows"  is  used  instead 
of  "is"  because  the  equivalent \ of  the  solution  depends  on  other 
factors  besides  its  composition,  jiln  general,  two  proofs  should 
be  used  in  every  set  of  "ten  bottles,  unless  several  tests  are  run 
in  rapid  succession,  when  one  proof  in  each  set  may  answer. 
Some  operators  run  an  independent  proof  occasionally  during 
the  day  and  omit  the  proof  in  the  sets,  but  this  proceeding  is 
objectionable. 

The  next  step  in  the  method  is  the  addition  of  100  c.c.  of  the 
standard  salt  solution  (improperly  termed  normal).  This  is  a 
very  simple  operation,  but  it  requires  the  utmost  care  and  atten- 
tion to  details  if  high  accuracy  is  desired.  Even  a  minute  varia- 
tion in  the  addition  will  make  a  serious  variation  in  the  fineness 
of  silver  shown. 

The  Stas  pipette  is  the  one  universally  used  in  the  Mints. 
It  is  a  simple  pipette  open  at  both  ends  and  securely  mounted 
on  a  wall  bracket.  The  upper  end  is  drawn  out  to  a  fine  open- 
ing and  is  provided  with  a  collar-cup  to  catch  the  drip.  The 
lower  end  is  comparatively  large  and  must  have  a  free  and 
smooth  discharge.  The  lower  end  is  connected,  by  means  of  a 
removable  rubber  tube  provided  with  a  pinch  cock,  with  an  ele- 
vated tank  containing  the  salt  solution.  No  stop  cocks,  floats, 
or  graduations  of  any  kind  can  be  used  on  or  in  the  pipette  if 
rapid  work  is  to  be  done. 

In  operation,  the  rubber  tubing  is  slipped  over  the  lower  end 
and  the  pinch  cock  opened.  As  soon  as  the  solution  comes  out 
of  the  upper  end  of  the  tube,  it  is  closed  by  the  first  finger  of 
the  left  hand  and  the  cock  closed.  The  operator  must  now  be 
sure  that  there  are  no  air  bubbles  in  the  pipette.  If  such  should 
appear  they  must  be  allowed  to  collect  at  the  top  of  the  pipette; 
the  pinch  cock  must  be  opened,  the  finger  momentarily  removed 
from  the  upper  end  of  the  pipette,  and  the  pinch  cock  closed 
again.  When  the  pipette  is  full  of  solution  and  the  pinch  cock 
closed,  the  rubber  tube  is  withdrawn  from  the  lower  end  of  the 
pipette.  This  end  must  now  be  carefully  examined  to  see  that 
there  is  no  surplus  solution  adhering  to  it  or  that  the  air  has  not 
commenced  to  ascend  the  tube. 

If  the  lower  end  of  the  tube  is  in  proper  condition,  the  silver 
bottle  is  now  placed  directly  under  it,  the  finger  removed  from 
the  upper  end,  and  the  solution  allowed  to  flow  out  rapidly  in  a 


150  ANALYSIS  OF  COPPER 

smooth  solid  stream.  Just  as  soon  as  the  flow  stops,  the  bottle 
must  be  removed.  It  is  absolutely  fatal  to  accuracy  to  attempt 
any  adjustment  of  the  drip  of  the  pipette.  There  should  be 
only  just  easy  clearance  between  the  bottom  of  the  pipette  and 
the  top  of  the  bottle.  The  pipette  is  supposed  to  contain  100  c.c. 
and  it  is  desirable  that  it  should  be  fairly  accurate,  but,  abso- 
lute accuracy  is  not  necessary.  The  absolutely  essential  point 
about  it  is  that  it  should  deliver  exactly  the  same  amount  of 
solution  to  each  one  of  the  ten  bottles  in  a  set.  The  amount 
may  not  be  quite  100  c.c.,  or  may  vary  slightly  from  summer  to 
winter,  but  it  should  not  vary  from  the  first  to  the  last  bottle 
in  a  set.  It  is  a  good  plan  to  fill  and  empty  the  pipette  a  few 
times  before  filling  the  set.  After  withdrawing  the  bottle  from 
under  the  pipette,  the  stopper  is  dipped  in  distilled  water  and 
inserted  in  the  neck  of  the  bottle  with  care.  Having  filled  the 
set,  the  carefully  stoppered  bottles  are  placed  in  a  shaker  and 
agitated  from  three  to  five  minutes  to  settle  the  precipitate. 
The  bottles  are  next  placed  on  a  black  shelf,  technically  called 
"a  board,"  with  a  black  background  about  as  high  as  the 
shoulder  of  the  bottle  and  about  three  inches  in  the  rear,  the 
whole  being  installed  in  a  window,  preferably  with  a  northern 
exposure. 

Modifications.  —  Beyond  this  point  there  are  slight  differences 
in  the  manipulation  in  different  laboratories.  In  common  with 
many  volumetric  methods,  there  is  difficulty  in  determining  the 
end-point.  The  assays  are  finished  with  a  "decimal  solution," 
1  c.c.  of  which  neutralizes  1  mg.  of  silver.  In  many  descrip- 
tions the  operator  is  directed  to  add  decimal  salt  in  small 
amounts,  with  agitation  between  the  additions,  until  no  more 
precipitate  is  formed  by  further  addition.  Too  much  salt  has 
now  been  added,  and  this  excess  must  be  determined  by  the 
addition  of  small  amounts  of  decimal  silver  solution,  and  the 
amount  of  silver  present  in  the  metal  determined  by  balancing 
these  amounts.  This  method  is  open  to  two  serious  objections. 
When  exactly  the  proper  amount  of  salt  has  been  added  to  throw 
out  all  of  the  silver  present,  equilibrium  results,  which  is  dis- 
turbed by  the  addition  of  either  reagent  with  the  separation  of 
a  precipitate.  This  obscures  the  end-reaction.  These  alternate 
dosings  and  shakings  consume  too  much  time  for  rapid  work, 
and  after  repetitions,  the  solution  does  not  clear  well. 


WORK  OF   THE  ELECTROLYTIC  REFINERY  151 

In  the  Mint  service,  therefore,  operators  "read  the  cloud" 
instead  of  repeatedly  dosing  ,the  solution.  This  operation  is  far 
more  rapid,  but  requires  a  gre$fc  deal  of  skill  and  constant  prac- 
tice to  yield  the  best* results.  In  reading  the  cloud,  after  the 
addition  of  100  c.c.  of  standard  salt  solution  and  shaking,  a 
measured  amount  of  1  or  .5  c.c.  of  decimal  salt  solution  is 
added  to  each  bottle.  The  delivery  end  of  the  pipette  is  placed 
against  the  neck  of  the  bottle  as  far  down  as  possible  and  the 
solution  allowed  to  flow  gently  down  the  side  so  that  it  will 
remain  on  the  surface  of  the  solution  with  the  minimum  amount 
of  mixing;  by  a  slight  rotary  motion  of  the  hand  the  decimal 
solution  is  then  mixed  with  the  upper  portion  (about  one-third) 
of  the  bottle  solution.  This  produces  a  cloud  of  silver  chloride 
in  the  solution,  and  the  next  step  is  based  on  the  appearance  of 
this  cloud.  Here  the  skill  and  visual  condition,  together  with  the 
personal  equation,  of  the  operator  are  of  the  utmost  importance. 

If  the  cloud  be  very  heavy,  two  or  more  portions  of  the 
decimal  salt  are  added,  the  amount  depending  on  the  density 
of  the  cloud,  and  the  bottles  shaken  in  the  machine  again.  If 
the  cloud  is  light,  only  one  dose  of  decimal  is  used,  and  the 
bottle  is  again  shaken  by  hand  to  bring  more  of  the  solution 
into  reaction  and  again  examined.  As  the  result  of  this  treat- 
ment, one  dose  of  decimal  may  be  used,  or  the  bottle  may  be 
shaken  by  hand  again  to  bring  the  balance  of  supernatant  solu- 
tion into  reaction.  Here  again  a  dose  of  decimal  solution  may  be 
used  or  the  final  reading  of  the  cloud  may  take  place.  In  the 
final  reading  the  operator  estimates  from  the  density  of  the  cloud 
what  portion  of  the  dose  of  decimal  solution  was  used  up  in 
precipitating  the  silver.  Many  operators  estimate  to  .25  c.c., 
others  claim  to  be  able  to  estimate  to  .1  c.c.,  but  Mr.  Dewey's 
figures  indicate  that  reading  to  .1  c.c.  on  standard  (900)  metal 
is  not  profitable  (loc.  cit.). 

All  of  the  bottles  are  eventually  brought  down  to  the  final 
cloud,  and  at  the  end  the  amount  of  decimal  solution  added 
to  each  bottle  is  recorded.  The  records  of  the  assays  are  then 
compared  with  the  proofs  and  the  fineness  of  the  samples  de- 
termined. The  actual  fineness  is  shown  entirely  by  the  amount 
of  decimal  solution  as  compared  with  the  amount  of  decimal 
required  by  the  proof.  It  is  entirely  independent  of  the  amount 
of  standard  solution  used.  Therefore,  in  determining  the  fine- 


152  ANALYSIS  OF  COPPER 

ness  of  a  sample  we  simply  compare  the  amount  of  decimal  used 
with  that  in  the  proof,  making  allowance  for  the  .5  mg.  addi- 
tional silver  in  the  proof  above  the  silver  in  1115  mg.  of  metal 
at  the  exact  standard  of  900,  and  taking  into  consideration  the 
weight  of  sample  used.  For  instance,  if  the  sample  required 
.5  c.c.  less  than  the  proof,  the  sample  would  be  reported  at  900. 
This  is  not  strictly  exact  because  .25  c.c.  of  decimal  salt  solu- 
tion equals  .25  mg.  of  silver,  but  .25  mg.  is  only  .22  fine  on 
1115  mg.  and  .5  would  be  only  .44  fine.  In  general,  however, 
the  finenesses  are  read  directly  from  the  difference  between  the 
sample  and  the  proof,  and  in  .25  of  a  cubic  centimeter.  Prac- 
tically one-half  is  deducted  from  the  amount  of  "decimal" 
used  on  the  proof  and  it  is  called  standard  (900).  Then  for 
each  quarter's  difference  for  standard  the  assayer  adds  or 
subtracts  from  each  900  according  to  this  tabulation : 

For£..                             ..0.2  Forf..                         ..1.3 

"    | 0.4  "    1 1.5 

"    f 0.7  "    | 1.8 

"     f 0.9  "    f 2.0 

| 1.1  "  V0 2.2 

A  second  method  of  determining  the  end-point,  which  appears 
to  be  even  more  exact  but  requires  more  time,  consists  in  adding 
only  .25  c.c.  of  the  decimal  solution  after  machine  shaking,  then 
estimating  the  number  of  quarters  the  solution  will  stand.  These 
are  added  and  the  bottles  shaken  in  the  machine.  This  is  con- 
tinued until  the  quarter  added  after  shaking  produces  no  pre- 
cipitate, in  which  case  the  last  quarter  is  not  counted,  or  else 
such  a  slight  precipitate  is  produced  that  the  quarter  is  counted 
but  the  bottle  is  not  shaken  again.  The  reading  of  the  results 
is  the  same  as  before  described.  In  both  these  methods  great 
care  is  exercised  to  avoid  the  addition  of  so  much  salt  as  to 
require  any  reverse  titration  with  silver  solution. 

7.  Titration  of  Silver  in  Bullion.  —  Owing  to  the  fact  that 
constant  practice  is  required  to  enable  the  operator  to  check 
by  the  original  Mint  method  within  1  fine  on  a  sample  of  silver 
bullion,  the  following  titration,  devised  by  F.  Andrews,  is  better 
adapted  to  the  work  of  electrolytic  refineries.  This  method  of 
titration  is  a  modification  of  the  original  one  attributed  to 
Volhard  l  or  Charpentier.2 

1  J.  Pract.  Chem.  1874.  2  Compt.  Rend.  1871. 


WORK  OF   THE  ELECTROLYTIC  REFINERY  153 

Weigh  out  2  grams  of  fine  clean  drillings,  or  granulations,  and 
2  grams  of  1000  fine  proof  silyef  (standardized  by  U.  S.  Mint 
or  Assay  Office)  into  200  c.c.  graduated  flasks  with  long  necks. 
Dissolve  in  35  c.c.  of  (1*:  2)  nitric  acid,  boil  off  red  fumes,  and 
cool  to  room  temperature.  In  all  the  subsequent  operations 
the  standards  must  be  treated  just  like  the  bullion.  Run  in 
without  draining,  by  an  automatic  pipette  100  c.c.  of  a 
standard  solution  of  hydrochloric  acid  of  such  strength  that 
100  c.c.  precipitates  a  few  milligrams  less  than  2000  mg.  of 
silver.  Cork  the  flask  with  a  rubber  stopper  and  shake  until 
the  solution  is  clear.  Wash  off  the  stopper  and  neck  of  the 
flask  and  make  up  to  the  200  c.c.  mark;  cork  the  flask  again 
with  a  dry  rubber  stopper  and  shake  well  to  mix  the  contents. 
If  the  flask  is  not  of  a  design  to  permit  mixing  by  shaking, 
pour  the  contents  three  times  into  a  dry  beaker.  Let  the  silver 
chloride  settle  for  one  hour  and  then  measure  off  100  c.c.  of 
clear  solution  by  means  of  a  measuring  tube  into  an  Erlen- 
meyer  flask.  Add  3  c.c.  of  a  saturated  solution  of  iron  alum  as 
an  indicator  and  titrate  with  a  standard  solution  of  ammonium 
thiocyanate.  1  c.c.  of  the  thiocyanate  finishing  solution  equals 
.001  gram  of  silver;  the  end-point  is  a  reddish  brown.  A  com- 
parison of  the  quantity  of  reagent  used  in  titrating  the  sample 
and  the  proof  determines  the  fineness. 

7a.  Second  Modification1  (F.  P.  Dewey). —  Impure  auriferous 
bullions  are  titrated  with  thiocyanate  alone,  finishing  with  decimal 
strength.  Wrap  .5  gram  in  1  g.  lead  foil  and  fuse  under  potas- 
sium cyanide  in  a  scorifier  with  10  parts  of  cadmium.  Boil  in 
60  g.  of  32°  nitric  acid  and  dilute  with  100  c.c.  water  before 
adding  the  indicator.  Silver  chloride  reacts  slowly  and  mercury 
or  palladium  interfere.  Moderate  amounts  of  copper  and  plati- 
num do  not.  Cobalt  and  nickel  obscure  the  end-point,  but  the 
back-titration  may  be  employed.  Ferrous  iron  and  nitrous  oxide 
must  be  absent. 

SECTION  2A.      THE    CONTROL    OF    ELECTROLYTES   AND   ANODE 
SLIMES  IN  THE  ELECTROLYTIC  REFINERY 

8.  Free  Sulphuric  Acid  in  the  Electrolyte.  —  The  vat  solu- 
tion is  conveniently  delivered  to  the  laboratory  in  large  glass- 

1  J.  Ind.  and  Eng.  Chem.  6  (1914),  650,  728;  Abstract,  Eng.  and  Min. 
Jour.  99,  355. 


154  ANALYSIS  OF  COPPER 

capped  jars,  is  cooled  to  room  temperature,  and  the  specific 
gravity  (or  density)  taken  with  the  hydrometer.  All  large  re- 
fineries use  practically  the  same  method.  (Most  of  the  description 
is  due  to  J.  Klein.)  The  solutions  required  are : 

(a)  Normal    Solution    of    Sulphuric     Acid.  —  49.04     grams 
H2SO4,  or  its    equivalent    of    pure   (93    per  cent)   acid,   is  dis- 
solved  in    500    c.c.    of   distilled    water,    cooled  and   diluted   to 
1000    c.c.   at    70°   Fahr.    with     distilled     water.      This   is    first 
standardized  against  sodium  carbonate. 

(b)  Normal  Sodium  Carbonate.  —  26.5    grams  of   anhydrous 
chemically    pure    sodium    carbonate    is    dissolved    in    distilled 
water  at  70°  Fahr.   and  diluted  to    500  c.c.     The  indicator  is 
made    by     dissolving    .05    gram     of     dimethylamidoazobenzol 
(methyl   orange)  in  75  c.c.  of   95   per  cent  alcohol.     The  nor- 
mal   solution    of   sulphuric   acid    is    also   valued    by  measuring 
out    a    definite   amount,    say    20  c.c.,    adding    a    little    hydro- 

.  chloric  acid,  and  precipitating  with  barium  chloride,  then 
weighing  the  filtered  and  ignited  sulphate  of  barium.  This 
serves  as  a  check. 

(c)  Standard  Potassium  Hydroxide.  —  Thirty  (or  sixty)  grams 
of  Merck's  purified  sticks  are  dissolved  in  water  and  diluted  to 
1000  c.c.  and  standardized  against  the  sulphuric  acid  when  made. 

(d)  Standard    Solution    of    Copper    Electrolyte.  — 100    grams 
of   pure   copper  sulphate  crystals   and    147  grams  of  sulphuric 
acid    (d.,   1.835)    are    dissolved    in   500   c.c.    of   water,    cooled, 
and  diluted  to  1000  c.c.     This  is  standardized  by  precipitating 
the  copper  from  a  measured  amount  by  electrolysis  and  cal- 
culating the  value  in  copper.    Solution  is  kept  in  stock  and  used 
to  standardize  both  the  potassium  hydroxide  and  cyanide. 

Determination.  —  Take  two  5  c.c.  portions  of  the  sample  of 
electrolyte,  add  20  c.c.  of  water  and  3  to  8  drops  of  indicator, 
and  titrate  with  the  standard  solution  of  potassium  hydroxide, 
and  then  calculate  the  amount  of  free  acid  in  grams  per  liter. 
By  dividing  the  result  by  the  specific  gravity,  the  percentage 
of  acid  by  weight  is  easily  obtained. 

9.  The  Mansfeld  Process  of  Titration.  —  H.  Koch  has  modi- 
fied the  old  method  of  Kieffer  to  make  its  titer  definite.  The 
titrating  solution  is  made  by  dissolving  a  known  weight  of  the 
complex  cupric-ammonium  sulphate  in  water:  The  process  de- 
pends on  the  double  decomposition  which  this  salt  undergoes 


WORK  OF  THE  ELECTROLYTIC  REFINERY  155 

by  the  action  of  free  acid,  the  latter  uniting  with  the  ammonia, 
setting  free  ammonium  sulphate  and  cupric  sulphate,  both  of 
which  dissolve  clear  in  the  fluid. 

CuS04  +  4NH3  +  2  H2S04  ^  CuS04  +  2(NH4)2S04. 

On  saturation  by  free  acid,  the  ammonium  in  the  complex  salt 
goes  to  the  acid  radical  in  the  CuSO4  and  precipitates  copper 
hydroxide.  As  a  sign  of  the  end-reaction,  there  occurs,  with  the 
slightest  excess,  a  distinct  turbidity  of  the  liquid.  The  titer  is 
not  empirical  but  systematic;  the  quantity  weighed  is  determined 
by  the  formula  of  the  hydrated  complex,.  CuO,  SO3(NH3)4.(OH)4. 
Dividing  the  molecular  weight  by  2  gives  122.72  parts.  If  two 
molecules  of  sulphuric  acid  exactly  neutralize  one  molecule  of 
cupric  ammonium  salt,  the  weight  of  the  standard  "salt"  to  be 

122  72 

taken  is  - — '- —  or  61.36  grams  per  liter.     Actually  the  standard 
2 

solution  of  commercial  salt  requires  65  grams  on  account  of  its 
moisture.  An  improvement  is  also  effected  by  the  addition  of 
6  grams  of  ammonium  sulphate.  The  fluid  then  remains  clear 
for  a  month  and  its  titer  unaltered,  provided  that  good  un- 
crushed  crystals  of  the  complex  salt  are  employed. 

The  two  weighed  salts  are  dissolved  in  about  800  c.c.  of 
cold  water,  filtered,  and  diluted  to  one  liter  with  the  distilled 
water  after  standing  for  twelve  hours.  The  water  must  be 
freed  from  carbon  dioxide  before  use  by  long  boiling.  The  addi- 
tion of  the  ammonium  sulphate,  as  recommended,  exercises  no 
subsequent  influence  on  the  solubility  of  the  cupric  oxide,  so 
that  the  results  of  titrations  for  free  acid  performed  under  vary- 
ing conditions  check  very  closely.  Method  8  is  preferred  in 
the  United  States,  as  the  end-point  is  so  distinct,  and  the  nor- 
mal alkali  may  be  more  accurately  standardized. 

COPPER  IN  ELECTROLYTES 

10.  Titration  by  Potassium  Cyanide.  —  The  time  which  may 
be  allowed  for  a  test  and  the  percentage  of  impurity  in  the 
electrolyte  will  naturally  govern  the  choice  of  methods  from 
those  to  be  described. 

Cyanide.  —  As  much  as  60  grams  per  liter  have  been  used, 
but  the  writer  prefers  a  solution  of  24.5  grams  of  98  per  cent 
salt,  or  24  grams  of  pure  salt,  per  liter. 


156  ANALYSIS  OF  COPPER 

This  solution  may  be  standardized  against  the  standard 
electrolyte,  or  against  a  solution  made  by  dissolving  .2  gram  of 
99.95  per  cent  copper  in  pure  nitric  acid  (d.,  1.2).  Evaporate 
to  dry  ness,  dissolve  in  water,  add  10  c.c.  of  strong  ammonia, 
cool,  and  titrate  with  cyanide,  then  calculate  its  value  in  copper. 
The  titration  of  this  standard  should  be  made  in  the  same  time- 
and  conditions  as  the  tests  of  works  samples. 

Vat  Solutions.  —  Take  two  5  c.c.  portions  of  the  electrolyte, 
add  20  c.c.  of  water,  5  c.c.  of  nitric  acid,  and  heat  nearly  to 
boiling  to  oxidize  ferrous  iron,  etc.  Now  add  10  c.c.  of  am- 
monia (d.,  .9),  cool  to  room  temperature,  and  titrate  with 
cyanide,  observing  the  same  rules  as  in  standardization.  Occa- 
sionally check  by  electrolysis. 

11.  Titration    by   Potassium   Permanganate    for    Copper.  - 
R.   Cobeldick  precipitates  copper  as  thiocyanate  and  then  redis- 
solves  and  titrates. 

1  c.c.  of  electrolyte  is  run  into  a  150  c.c.  beaker,  diluted 
to  100  c.c.,  heated  to  boiling,  and  treated  with  10  to  15  c.c.  of 
sodium  sulphite  (200  grams  per  liter),  then  with  5  to  10  c.c.  of 
potassium  thiocyanate  solution  (40  grams  per  liter).  The  liquid 
is  boiled  for  two  minutes,  allowed  to  stand  for  ten  minutes, 
filtered,  the  filter  washed  four  times  with  hot  water,  and  the 
contents  decomposed  with  hot  8  per  cent  sodium  hydroxide. 
The  copper  precipitate  is  washed  well  with  hot  water,  the  solu- 
tion made  acid  with  sulphuric  acid,  boiled,  and  titrated  with 
standard  potassium  permanganate  (1  c.c.  =  .002  gram  of  copper). 
The  copper  value  X  4  =  the  blue  vitriol  (CuSO4.5H2O).  The 
objection  to  this  scheme*  is  the  manipulation,  and  the  small 
sample  treated,  but  the  principle  of  separation  is  valuable  for 
impure  electrolytes. 

12.  Mansfeld  Method  of  Titration  with  Sodium  Sulphide.  - 
In  order  to  render  the  end-point  distinct,  the  solution  is  shaken 
during  titration  with  a  large  quantity  of  chloroform,  or  better, 
carbon  tetrachloride.     It  is  necessary  to  keep  the  copper  within 
certain  limits.     If  copper  solutions  are  too  rich,  the  results  are 
uncertain,  hence  the  solutions  must  be  divided  so  that  not  over 
50  c.c.  of  sulphide  are  used.     If  a  works  sample  is  to  be  tested, 
25  c.c.  are  diluted  to    250  c.c.,  from  which    25  c.c.    (2.5-gram 
samples)  are  withdrawn  for  titration.    The  conditions  of  dilution 
and  acidification  should  be  followed  exactly  as  described. 


WORK  OF   THE  ELECTROLYTIC  REFINERY  157 

The  test  liquid  is  placed  in  a  stoppered  flask  of  about  300  c.c. 
capacity,  20  c.c.  of  (25  Be.)  Sulphuric  acid  added,  diluted  with 
water  until  the  flask  js  half  fall,  and  finally  60  c.c.  of  car- 
bon tetrachloride  poured  in.  Some  standard  sodium  sulphide  is 
allowed  to  flow  in,  the  flask  stoppered  and  shaken  vigor- 
ously. The  supernatant  liquid  becomes  water-clear.  The 
shaking  is  repeated  with  each  addition  of  sulphide,  until  the 
last  addition  causes  only  the  slightest  turbidity.  The  clarifica- 
tion proceeds  slowly  with  old  solution,  containing  thiosulphate 
formed  by  oxidation.  So  it  is  recommended  that  illuminating 
gas  be  kept  in  the  bottle  above  the  solution,  charging  the  solu- 
tion through  the  lower  tubulure  of  the  stock  bottle. 

The  sodium  sulphide  is  prepared  as  an  approximately  nor- 
mal solution.  The  requisite  sodium  hydroxide  is  first  dis- 
solved in  500  c.c.  of  water,  then  divided  in  two  equal  parts, 
and  one-half  saturated  with  hydrogen  sulphide.  The  other  half 
is  now  added  and  the  whole  diluted  to  one  liter.  The  solution  is 
standardized  against  pure  copper.  The  process  is  also  used,  in 
Germany,  for  lean  slags  or  ores  of  lead,  but  is  not  favored  in 
the  United  States. 

13.  Copper    in  Vat    Solution   by   Electrolysis.  —  Instead    of 
dissolving   and   titrating   sulphocyanate  of   copper  F.  D.  Green- 
wood   redissolves  and    elect rolyzes  the   precipitate.      10   to  20 
c.c.  of  electrolyte  are   treated   as  in  11,  the  white  salt  filtered, 
washed,  dissolved  in  acid    as    described   in  Chapter  X,  method 
4,  and  the  solution  electrolyzed  for  copper. 

\  CHLORINE  IN  ELECTROLYTES 

14.  Combination  Method.  —  According  to  J.  Klein,  500  c.c. 
of  electrolyte  should  be  treated  with  40  c.c.  of  nitric  acid  (d., 
1.42),  stirred,   and  allowed  to  oxidize.     Then  add   1   c.c.   of  a 
normal  solution  of  silver  nitrate,  allow  to  stand  in  a  warm  place 
for  forty-eight  hours,  filter,  cupel  the  silver  chloride,  and  calcu- 
late the  chlorine  by  multiplying  the  weight  of  silver  by  the  fac- 
tor .32858.     Instead   of   cupeling,  the  chloride  may  be  filtered 
from  solution  on  an  asbestos  felt,  which  has  been  extracted  with 
nitric  acid,  dried,  and  weighed  before  use.     The  silver  chloride 
is  finally  dried  at  130°  C.  and  weighed  as  chloride.     In  order  to 
weigh  directly,  the  original   electrolyte  should  be  clear  and  free 
from  all  suspended  sediment. 


158  ANALYSIS  OF  COPPER 


DETERMINATION  OF   OTHER  IMPURITIES 

15.  Separation  of  Copper  and  Antimony  from  other  Metals. 
—  To  10  c.c.  of  electrolyte  add  200  c.c.  of  water  and  15  c.c.  of 
sulphuric  acid  (d.,  1.835),  pass  hydrogen  sulphide  to  precipitate 
metals,  and  when  the  reaction  is  complete,  filter,  wash  well  with 
hot  water,  and  place  the  nitrate  on  the  hot  plate  to  evaporate 
for   the   determination   of   iron,  aluminum,    nickel,   and    cobalt. 
The  following  method  is  the  one  adopted  by  J.  Klein,  with  some 
modifications  by  the  author. 

Transfer  the  sulphides  to  a  beaker  and  digest  with  15  c.c. 
of  a  saturated  solution  of  sodium  monosulphide  diluted  with 
100  c.c.  of  water.  Heat  to  150°  Fahr.  for  about  an  hour,  filter 
while  hot,  and  wash  well  with  hot  water  containing  a  little  hydro- 
gen sulphide.  The  paper  with  precipitate  is  transferred  to  the 
beaker  in  which  the  hydrogen  sulphide  treatment  was  performed, 
treated  with  100  c.c.  of  nitric  acid  (d.,  1.2),  and  placed  on 
the  steam  plate  until  all  copper  is  dissolved.  Do  not  heat  too 
high,  as  the  filter  paper  will  become  too  fine  and  retard  the  filtra- 
tion. Filter  and  wash  well.  To  the  filtrate  add  5  c.c.  of  pure 
sulphuric  acid  (d.,  1.84),  evaporate  to  fumes,  dilute,  add  1  c.c. 
of  nitric  acid,  and  electrolyze  for  copper,  if  a  check  is  desirable 
on  the  cyanide  titration. 

Antimony.  —  The  sodium  sulphide  extract  is  treated  with  an 
excess  of  dilute  sulphuric  acid,  the  arsenic  and  antimony  filtered 
off,  and  separated  by  digestion  with  hydrochloric  acid  (d.,  1.16). 
Filter  off  the  arsenious  sulphide,  wash  well,  add  about  1  gram 
of  sodium  chloride  and  2  grams  of  tartaric  acid,  evaporate  to 
about  50  c.c.  to  expel  hydrochloric  acid,  and  dilute  with  water 
to  200  c.c.  Pass  hydrogen  sulphide,  allow  to  settle,  filter  off  the 
sulphide  of  antimony,  and  dissolve  it  in  ammonium  sulphide 
by  digesting  the  filter  with  the  reagent,  or  by  dropping  some 
around  the  filter  and  then  treating  with  hot  strong  ammonia. 
Evaporate  to  a  small  bulk,  acidify  with  nitric  acid,  evaporate, 
add  nitric  again,  transfer  to  a  small  weighed  porcelain  crucible, 
evaporate  twice  with  nitric  acid,  heat  the  residue,  and  weigh  as 
antimony  tetroxide. 

16.  Iron,  Aluminum,  Cobalt,  and  Nickel.  —  The  filtrate  from 
the  hydrogen  sulphide  separation  is  evaporated  to  drive  off  the  hy- 


WORK  OF   THE  ELECTROLYTIC  REFINERY  159 

drogen  sulphide.  When  the  volume  has  been  reduced  to  100  c.c., 
add  50  c.c.  of  strong  hydrogen  peroxide  and  evaporate  to 
white  fumes,  cool,  add  50  c.c.  o&  water  and  evaporate  to  white 
fumes  again,  repeat  the  operation,  and  then  dissolve  in  water. 
Make  the  solution  slightly  alkaline  with  ammonia,  boil,  and 
filter  off  the  alumina  and  ferric  hydroxide.  Finally,  wash,  dry, 
ignite  and  weigh  the  precipitate,  and  calculate  its  amount 
in  grams  per  liter.  Evaporate  the  filtrate  from  the  iron  to 
100  c.c.,  render  it  strongly  ammoniacal,  and  precipitate  the 
nickel  and  cobalt  together  on  weighed  platinum  electrodes,  with 
a  current  density  of  .75  to  1  ampere.  A  strong  solution  of 
sodium  sulphide  may  be  used  to  test  the  completeness  of  the 
precipitation. 

Titration  of  the  Iron.  —  Fuse  the  weighed  precipitate  of 
alumina,  etc.,  with  sodium  carbonate,  treat  the  fused  mass  with 
hot  water,  make  the  liquid  acid  with  sulphuric  acid,  reduce  the 
iron  by  any  reliable  method,  and  titrate  with  standard  potassium 
permanganate.  (See  Chapter  V.) 

(b)  Alternative  Method  for  Nickel.  —  The  copper  and  other 
similar  metals  are  removed  by  hydrogen  sulphide,  as  in  the 
previous  treatment  (15).  Boil  the  filtered  solution  in  a  flask  for 
ten  to  twenty  minutes  with  5  c.c.  of  a  mixture  of  bromine  and 
hydrochloric  acid,  then  add  5  c.c.  of  nitric  acid  and  boil  one 
minute  longer.  Cool  the  solution,  add  an  excess  of  ammonia, 
filter  into  a  No.  2  beaker,  and  wash  the  ferric  hydroxide  thor- 
oughly with  hot  water.  Add  10  c.c.  of  saturated  ammonium 
carbonate  solution  to  the  filtrate  and  electrolyze  for  nickel  with  a 
low  current  of  only  .1  to  .15  ampere  per  square  decimeter  of  im- 
mersed cathode  surface.  This  modification  is  due  to  Cobeldick. 

17.  Arsenic  in  Electrolyte.  —  Place  5  to  25  c.c.  of  %  electrolyte 
in  a  300  c.c.  Erlenmeyer  flask,  which  is  connected  to  a  vertical 
8-inch  Allihn  glass  condenser  by  a  glass  tube  which  has  a  slight  rise 
of  one  inch  after  leaving  the  flask.  (See  Fig.  14,  Chapter  XII.) 
The  flask  is  mounted  on  a  thin  plate  heated  by  gas  or  electricity. 
Add  to  the  flask  2  grams  of  ferrous  chloride,  or  sulphate,  and 
close  the  flask  with  the  rubber  stopper. 

Pour  through  a  60  c.c.  separatory  funnel  10  c.c.  of  sulphuric 
acid  (d.,  1.84),  then  follow  with  50  c.c.  of  hydrochloric  acid 
(d.,  1.16),  and  distill  to  about  25  c.c.  volume.  Add  30  c.c.  of 
hydrochloric  acid,  1  c.c.  of  a  10  per  cent  solution  of  hypophos- 


160  ANALYSIS  OF  COPPER 

phorous  acid,  and  distill  down  to  25  c.c.  again.  Repeat  the  same 
addition  and  distillation,  when  the  arsenic  should  all  be  in  the 
distillate.  To  prevent  the  distillate  sucking  back  into  the  flask, 
the  bottom  of  the  condenser  should  be  kept  just  far  enough  below 
the  surface  of  water  in  the  receiver  to  effect  a  seal  for  the  vapors 
evolved.  Make  the  total  distillate  alkaline  with  ammonia,  then 
just  acid  with  dilute  sulphuric  acid,  using  litmus  paper  as  an 
indicator.  Cool  in  a  basin  of  water  to  room  temperature  and 
make  alkaline  with  ten  grams  of  sodium  bicarbonate,  or  use  a 
considerable  excess  of  a  saturated  solution  of  the  same  salt. 

The  volume  of  the  solution  is  now  about  400  to  500  c.c. 
Pour  off  about  100  c.c.  of  this  solution  into  a  graduate  (if  rich 
in  arsenic).  Titrate  the  whole  or  the  aliquot  portion  with  a 
standard  solution  of  iodine  and  potassium  iodide.  1  c.c.  equals 
.001  gram  of  arsenic  (21,  Chapter  III). 

A  hydrochloric  acid  made  by  the  electrolytic  process  is  the 
best  suited  to  such  work. 

ANALYSIS   OF  ANODE   MUD,  OR  SLIMES 

Preparation.  —  Electrolytic  slimes,  as  received,  are  washed 
free  from  all  soluble  sulphates,  then  dried  and  ground  to  pass 
a  screen  of  60  meshes  to  the  linear  inch.  The  next  four  methods 
are  due  to  Klein. 

18.  Determination   of   Arsenic.  —  Weigh    1    gram    of    dried 
sample,  dissolve  in  nitric  acid,  add   15  c.c.   of  sulphuric  acid, 
evaporate  to  white  fumes,  cool,  add  50   c.c.   of   water,   repeat 
the  evaporation  to  fumes  twice,  then  transfer  to  the  distilling 
flask,   and   distill    exactly    as   in   the   preceding    method    (17). 
Titrate  the  arsenic. 

19.  Gold  and  Silver  in  Boiled  Slimes  from  Lake  Copper.  - 
Place  5  grams  of  test  lead  on  a  cupel,  weigh  out  .2  gram  of 
sample  and  place  it  on  the  cupel,  add  5  grams  more  of  test  lead, 
mix,  cover  with  test  lead,  cupel  directly,  and  weigh  the  button. 

(6)  Silver  in  (Lake)  Raw  Slimes.  —  Place  15  grams  of  test 
lead  in  a  3.2  cm.  (2J  inch)  scorifier,  weigh  out  .5  gram  of  the 
slime,  place  it  in  the  scorifier,  add  15  grams  more  lead,  mix  the 
charge,  cover  with  test  lead,  add  a  little  litharge  and  borax 
glass,  and  scorify.  If  the  button  of  lead  is  too  hard,  rescorify 
with  the  addition  of  test  lead  and  a  little  borax;  cupel  and 
weigh  the  resulting  silver  button. 


WORK  OF  THE  ELECTROLYTIC  REFINERY  161 

20.  Silver  in  Slimes  from  Converter  Copper.  —  According  to 
Greenwood,  these  slimes  are  assayed  by  the  same  method  as 
given  for  Dore  bullion  containing  bismuth,  selenium,   and  tel- 
lurium, except  that  no  proof  is  run,  or  correction  made  on  slag 
and  cupel. 

21.  Insoluble  Matter.  —  Weigh  out  1  to  2  grams  of  dried 
slimes,  dissolve  in  nitric  acid,  and  filter  the  extract.     At  some 
works,  it  is  customary  to  determine  the  chlorides  in  this  material. 

Fuse  with  a  mixture  of  equal  parts  of  sodium  carbonate  and 
sulphur,  dissolve  the  fusion  in  water,  filter,  and  wash.  Heat  the 
residue  to  boiling,  with  nitric  acid  (d.,  1.2),  dilute  and  precipitate 
the  silver  with  hydrochloric  acid.  Stir,  heat,  and  decant 
through  a  filter,  keeping  the  silver  in  the  beaker.  Then  add 
hot  water  and  a  few  drops  of  hydrochloric  acid,  boil,  decant 
through  the  filter,  repeat  the  operation,  and  discard  the  silver 
chloride. 

22.  Lead.  —  Evaporate   the   filtrate   to    100   c.c.     Filter   off 
and  discard  any  silver  chloride  which  may  appear  at  this  time. 
Make  the  solution  alkaline  with  sodium  hydroxide  and  add  the 
solution   of    the    sodium    carbonate-sulphur   fusion   in   order  to 
precipitate  all  the  sulphides  of  the  copper  group.     Digest,  heat 
to  boiling,  filter,  and  reserve  the  filtrate  for  the  determination  of 
antimony  and  tin    (26).     Place  the   precipitate  in  the  beaker, 
dissolve  it  in  nitric  acid  (d.,  1.2),  wash  well,  add  to  the  filtrate 
10  c.c.  of  sulphuric  acid  and  evaporate  to  white  fumes.     Cool, 
add  water,  and  repeat  the  evaporation  twice.     Add  water  and 
alcohol  and  filter  off  lead  sulphate  and  insolubles.     Digest  the 
mass   with    ammonium   acetate   to   dissolve   the   lead   sulphate, 
filter,  and  wash;  then   add   an   excess  of  sulphuric  acid  to  the 
extract  to  precipitate  the  sulphate  of  lead.     Filter  on  a  weighed 
porcelain  Gooch  crucible,  ignite  carefully,  and  weigh. 

23.  Copper   Assay.  —  In   complete   analysis,    boil   down   the 
filtrate   from   the    lead,    neutralize   with   ammonia,    then    make 
acid  with  3  c.c.  of  sulphuric  and  2  c.c.  of  nitric  and  electrolyze 
for  copper. 

Copper  may  be  estimated  directly  in  an  original  solution  of  a 
2-gram  sample  of  the  slimes,  if  interfering  elements  are  first 
removed.  This  may  be  effected  by  the  addition  of  sodium 
sulphite  and  thiocyanate,  or  by  repeated  precipitation  with  excess 
of  ammonia  after  adding  6  grams  of  ferric  alum.  In  the  former 


162  ANALYSIS  OF  COPPER 

case  the  white  salt  of  copper  is  decomposed  with    nitric  acid. 
Electrolyze  or  titrate  as  directed  for  ores  in  Chapter  IV. 

24.  Cobalt  and  Nickel.  —  Instead  of  dissolving  the  original 
slime  sample  in  nitric  acid,  it  may  be  digested  two  to  three  hours 
with  aqua-regia  if  preferred  (Cobeldick).     Evaporate  to  dryness 
with  excess  of  sulphuric  acid  and  heat  to  white  fumes  to  expel 
all  the  hydrochloric  acid.     Take  up  the  dry  mass  with  water  and  a 
little  sulphuric  acid,  warm  until  all  soluble  matter  is  dissolved,  and 
filter  into  a  250  c.c.  beaker.     (If  the  solution  was  so  impure  that 
it  was  found  necessary  to  separate  the  copper  first  as  thiocyanate, 
the  excess  of  reagent  should  be  destroyed  before  any  attempt  is 
made  to  estimate  cobalt  and  nickel,  the  arsenic  and  selenium  be- 
ing removed  as  sulphides  — 22.) 

Determine  copper  by  electrolysis  and  separate  lead  as  already 
described.  Evaporate  the  filtrate  or  electrolyte  and  washings  to 
fumes  if  any  nitric  acid  is  present  in  the  assay.  About  5  c.c.  of 
sulphuric  acid  should  now  be  present,  unless  the  carbonate  modi- 
fication is  adopted. 

-Nickel  and  cobalt  are  then  obtained  from  the  solution. 
Boil  with  an  excess  of  ammonia,  filter  off  the  ferric  hydroxide, 
and  estimate  the  iron  by  weighing  the  ignited  oxide,  or  by  titra- 
tion  with  permanganate. 

Treat  the  filtrate  from  the  iron  with  20  c.c.  of  strong  am- 
monia, or  with  15  c.c.  of  a  saturated  solution  of  ammonium 
carbonate,  and  electrolyze.  With  sulphate  use  .5  ampere  per  sq. 
decimeter.  With  a  carbonate  solution,  the  current  should  be  no 
more  than  .10  to  .15  ampere.  Total  volume  100  c.c. 

25.  Antimony    and    Arsenic    in    Slimes.  —  To    the    alkaline 
filtrate  from  the  soda-sulphur  fusion  (21)  add  sulphuric  or  acetic 
acid  to  precipitate  the  arsenic,  tin,  and  antimony.     After  settling, 
filter,  wash,  dissolve  in  ammonium  sulphide,  and  evaporate  to 
dryness  on  the  steam  plate.     Separate  the  tin,  preferably,   by 
the  method  of  G.  W.   Thompson,   as  described  in  full  in  the 
analysis  of  copper,  Chapter  XIII.     The  residue  is  boiled  with 
equal  parts  of  ammonium  oxalate  and  oxalic  acid  solution  and 
treated  with  hydrogen  sulphide.     The  precipitate  is  filtered  off 
and  the  filtrate  reserved.     The  sulphides  of  arsenic  and  antimony 
are  then  separated  by  digestion  with  hydrochloric  acid  (1.16),  the 
antimony   oxidized,    ignited   in   porcelain,    and   weighed   as   the 
tetroxide. 


WORK  OF   THE  ELECTROLYTIC  REFINERY  163 

26.  Tin  is  separated  from  the  oxalic  acid  by  evaporation  to 
fumes  with  sulphuric  acid,  after  which  the  diluted  solution  is 
neutralized  with  ammonia,    acidified   with    acetic,   and   the   tin 
thrown  down  by  hydrogen  sulphide. 

Allow  to  settle,  filter  off  the  tin  sulphide,  wash  well,  place 
the  paper  and  contents  in  a  beaker,  add  nitric  acid  (d.,  1.2), 
evaporate,  repeat  this  operation  a  second  and  third  time,  or 
until  the  tin  is  completely  oxidized.  Filter  on  a  porcelain  Gooch 
crucible  fitted  with  an  asbestos  felt,  ignite,  and  weigh  as  stannic 
oxide,  SnO2.  Traces  of  selenium  will  be  mostly  volatilized. 

27.  Alternative    Method    for    Insoluble    Matter.  —  Take    a 
1-gram  sample  and  dissolve  in  nitric  acid,  then  filter,  wash,  and 
treat  the  residue  with  a  boiling  solution  of  ammonium  acetate 
until  the  lead  sulphate  is  extracted.     Dry  the  residue  and  care- 
fully ignite  it  in  a  platinum   crucible,   after  which  it  may  be 
weighed,  if  desired. 

Fuse  the  residue  with  sodium  carbonate  and  potassium 
nitrate  in  equal  parts,  dissolve  in  water,  transfer  to  a  casserole, 
add  hydrochloric  acid,  and  evaporate  to  dryness  below  110°C. 
Cool  the  residue,  and  repeat  the  addition  of  acid  and  evaporation 
a  second  and  third  time.  Finally,  take  up  with  100  c.c.  of  water 
and  20  c.c.  of  hydrochloric  acid,  boil,  filter,  wash  the  residue 
thoroughly,  ignite,  and  weigh. 

28.  Sulphur  in  Slimes.  —  Dissolve  1  gram  of  slimes  in  nitric 
acid,  boil,  dilute  the  solution,  filter  on  a  paper  filter,  and  wash 
the  residue.     Place  the  filtrate  on  a  hot  plate,  add  hydrochloric 
acid  in  sufficient  amount  to  precipitate  all  the  silver,  stir  well, 
filter,  and  wash  the  paper,  discarding  the  silver  chloride.     Evap- 
orate the  filtrate,  reserve  any  insoluble  residue,  and  fuse  it  with 
the  mixture  of  sodium  and  potassium  carbonate.     Transfer  the 
fusion  to  a  casserole  and  dissolve  it  in  water,  add  hydrochloric 
acid  carefully  in  excess,  evaporate  nearly  to  dryness,  dilute,  heat 
to  boiling,   and  filter,   adding  this  filtrate  to'  the  first  filtrate. 
Evaporate  the  whole  to  dryness,  and  if  any  silver  chloride  ap- 
pears on  dilution,  filter  it  off  and  discard.     Evaporate  twice  to 
dryness  with  dilute  (1  : 2)  hydrochloric  acid,  dissolve  in  the  same 
acid,  filter,  heat  to  boiling,  and  add  barium  chloride.     Settle, 
filter,  wash,  ignite,  and  weigh  the  sulphate. 

29.  Platinum  and  Palladium.  —  Some  slimes  contain  traces 
of  these  valuable  metals.     They  may  be  separated  from  gold 


164  ANALYSIS  OF  COPPER 

and  silver  by  dissolving  in  sulphuric  acid,  filtering  and  melting 
the  residue  by  crucible  fusion,  and  following  the  same  methods 
adopted  for  ores  (8,  9,  10,  Chapter  VIII). 

Selenium  and  tellurium  may  be  precipitated  from  a  sulphuric 
acid  solution  by  method  7,  Chapter  XII. 

SILVER  REFINERY  SLAGS 

30.  From  Bullion  Refining  Furnace.  —  The  sample  received 
may  consist  of  several  pounds  of  coarsely  crushed  slag  which  has 
been  reduced  from  a  larger  sample  in  the  electrolytic  depart- 
ment by  means  of  rolls  or  gyratory  mill.  Reduce  the  slag  to 
pass  a  sieve  of  60  meshes  to  the  linear  inch  (24  per  cm.),  weigh 
the  whole,  and  also  weigh  and  separately  assay  the  pellets  remain- 
ing on  the  sieves.  Dissolve  the  pellets,  or  a  weighed  portion, 
in  dilute  nitric  acid,  filter  off  the  residue  for  gold  assay,  then 
determine  silver  by  wet  method  and  copper  by  color  test. 

Assay  of  the  Fines  for  Silver  and  Gold.  —  A  portion  of  3  to  6 
grams  (.1  to  .2  A.  T.)  of  the  fines  may  be  melted  in  a  crucible 
with  about  40  grams  of  litharge,  30  grams  sodium  carbonate,  10 
grams  of  borax,  and  1.5  grams  of  flour.  After  pouring,  the  slag 
is  re-melted  in  the  same  crucible  with  a  little  soda  and  1  gram  of 
flour.  Cupel  the  two  lead  buttons  together. 

For  greater  accuracy,  the  large  lead  button  should  be  cupeled 
first  and  the  cupel  melted  up  with  the  second  crucible  fusion. 
If  preferred,  the  fines  may  be  directly  scorified  with  sufficient  lead 
and  .5  gram  of  borax. 

Assay  for  Copper.  —  Weigh  2  grams  of  fines  and  boil  in  a 
100  c.c.  platinum  dish  or  a  four-inch  casserole  with  the  following 
mixture :  15  c.c.  sulphuric  acid,  6  grams  potassium  bisulphate, 
5  c.c.  nitric  acid,  and  about  5  c.c.  hydrofluoric  acid.  The  latter 
should  be  added  quickly  and  mixed  by  rotation.  The  solution 
should  be  evaporated  to  dryness,  heated  to  fuming  for  half  an 
hour,  and,  if  the  residue  is  not  white,  treated  with  5  c.c.  of 
sulphuric  acid  and  5  c.c.  hydrofluoric  acid  and  boiled  until  the 
nickel  oxide  is  dissolved.  Dilute  and  precipitate  the  silver; 
then  filter. 

Determine  copper  by  method  23.  Other  impurities  are  also 
estimated  by  the  methods  for  slimes. 


CHAPTER  X 

THE   ELECTROLYTIC  REFINERY 

VALUATION   OF  BLISTER,   CONVERTER  SLABS,  AND  ANODES 
GOLD  AND  SILVER 

Preparation  and  Weighing  of  Samples.  —  The  sampling  of 
crude  metal  at  the  furnaces,  or  in  carloads  at  custom  works,  has 
been  described  in  Chapter  II.  The  final  subdivision  of  the 
sample  in  the  laboratory  to  the  assay  weight  is,  however,  equally 
important.  There  is  some  difference  of  opinion  as  to  the  neces- 
sity of  sifting  variable  material  before  division  into  " coarse"  and 
" fines"  to  be  separately  assayed.  From  written  opinions  and 
personal  experience,  it  is  evident  that  the  manner  in  which 
samples  are  cut  to  final  assay  weight  depends  on  the  character 
of  the  material  treated  in  each  laboratory. 

If  the  material  is  very  variable  or  non-homogeneous,  the 
sample  of  4  to  5  pounds  (1.8  to  2.2  kg.)  is  ground  to  pass  a  TV- 
inch  sieve  and  sifted  through  a  40-mesh  sieve  (15  holes  per  cm.). 
The  coarse  and  fines  are  then  weighed  and  the  required  number 
of  reserve  samples  put  up  with  proportionate  parts  of  coarse  and 
fines  in  separate  bags.  The  samples  for  assay  then  consist  of 
two  parts,  respectively  coarser,  and  finer,  than  the  40-mesh 
sieve.  In  weighing  for  the  gold  and  silver,  the  assay  is 
made  up  with  the  coarse  and  fines  in  proper  ratio,  but  the  copper 
assay  is  made  on  each  part  separately  and  the  correct  assay 
figured.1 

For  pure  and  fairly  homogeneous  •  material,  the  borings  are 
ground  as  before,  but  are  cut  directly  without  sifting  by  means 
of  a  split  sampler  or  riffle  with  i-inch  divisions.  Some  operators 
divide  to  two  samples  of  40  grams  each,  others  reduce  further 
until  a  portion  is  obtained  of  one  "assay  ton"  (29.167  grams) 

1  Method  used  by  Raritan  Works,  Ledoux  &  Co.,  and  Calumet  &  Hecla. 


166  ANALYSIS  OF  COPPER 

for  the  gold-silver  assay  and  80  grams  for  duplicate  electrolyses, 
which  will  include  the  proper  amounts  of  the  finer  and  coarser 
parts.  Samples  " dipped"  from  a  bottle,  or  from  a  layer  spread 
out  on  paper,  will  not  contain  the  correct  proportions  of  coarse 
and  fine  drillings.1 

Solubility  of  Gold.  —  It  is  now  generally  conceded  that  the 
old  nitric  acid  method  gives  low  results  for  gold.  According 
to  F.  P.  Dewey,2  even  the  purest  gold  is  slightly  soluble  in 
nitric  acid  if  boiled  for  some  time.  Dr.  E.  Keller  has  observed 
with  regard  to  gold  in  copper  bullion3  that  gold  is  soluble  in 
varying  degrees  in  nitric  acid,  the  solubility  diminishing  with 
faster  cooling  of  the  copper  and  reaching  a  minimum  when  the 
molten  bullion  is  quenched  in  cold  water,  although  a  deficit 
still  exists  as  compared  with  the  fire  assay.  Accordingly,  the 
fire  assay  was  generally  specified  for  gold  before  the  introduction 
of  the  mercury-sulphuric  acid  method.  There  is  one  advantage: 
the  fire  assay  by  scorification  is  applicable  to  all  grades  of 
copper. 

"  1.  Fire  Assay  for  Gold.4  —  Weigh  out  4  portions  of  borings 
of  .25  " assay  ton"  each  (7.5  grams),  mix  with  50  grams  of 
test  lead,  transfer  to  3-inch  Bartlett  scorifiers,  cover  with  40 
grams  of  test  lead,  and  add  about  1  gram  of  silica.  Scorify 
hot,  heating  at  the  finish  so  as  to  pour  properly.  Add  test 
lead  to  make  the  weight  of  button  plus  lead  equal  to  70 
grams,  add  1  gram  of  silica,  and  scorify  for  the  fifth  time. 
The  button  should  be  free  from  slag  and  weigh  14  grams. 
Cupel  at  a  temperature  to  feather  nicely  and  raise  the  heat  at 
the  finish.  Use  a  cupel  of  medium  hardness,  made  of  60-mesh 
bone-ash. 

-  Weigh  the  bead  and  place  it  in  a  test  tube,  add  about 
10  c.c.  of  nitric  acid  (1  acid  (d.,  1.42)  to  5  volumes  of  water). 
Place  the  tube  in  a  beaker  of  water  and  warm  until  action 
ceases,  then  bring  the  water  to  boiling.  Pour  off  the  acid  and 
wash  with  distilled  water  three  times,  then  transfer  the  gold  to 
a  porcelain  crucible,  dry,  anneal,  and  weigh.  The  two  results 
should  check  within  .02  Troy  ounce  per  ton  of  2000  pounds  — 

1  Method  used  by  U.  S.  Metals  Refining  Co.,  also  Ledoux  &  Co. 

2  J.  Am.  Chem.  Soc.  32,  318. 

3  Bull  80,  A.I.M.  E.  2093,  and  83,  2738. 

4  Smoot  &   Greenwood,    personal    communications  —  same   as   author's 
method. 


THE  ELECTROLYTIC  REFINERY  167 

the  average  figure  to  be  reported.  If  the  silver  contents  of  the 
bullion  are  low,  add  enough  «fine  silver  to  the  copper  borings 
before  the  first  scorification  to*  make  the  total  silver  in  the 

••* 

mixture  equal  to  about  eight  times  the  gold.  The  objection 
to  any  all-fire  method  is  the  small  size  of  the  sample. 

2.  Western   Assay   for    Gold    in    Crude    Copper.  —  In    this 
modification  the  sample  is  made  very  small  to  avoid  scorification, 
but  a  number  of  portions  are  taken  from  each  package,  usually  ten 
portions  of  .05  assay  ton  each.     Place  them  directly  in  cupels.     Fill 
the  cupels  with  test  lead.     Open  the  cupellation  at  a  very  high 
heat,  having  very  little  coal  on  the  grate  bars.     Reduce  the  heat 
very  quickly  and  cupel  at  a  moderate  temperature.    Part  and  weigh 
the  beads  in  two  sets  of  five,  if  preferred.     The  cupels  used  are 
1.5  inches  (3.8  cm.)  in  diameter  and  1.12  inch  (3.8  cm.)  in  height.- 

3.  The     Mercury-Sulphuric     Acid     Method.1  —  This     is     a 
standard  assay  for  gold,  silver,  and  platinum  which  is,  however, 
applicable  only  to  high   converter  blown  metal,  or  well-refined 
copper.     It    tends    to    give    high    silver   results,    owing   to    the 
presence  of  copper  in  the  silver  bead  (Greenwood).     According 
to  the  experience  of  several  laboratories,  the  acid  process  with 
amalgamation  is  the  best  universal  method. 

The  modification  employed  by  Greenwood,  Smoot,  and  the 
author  is  as  follows  :  —  Weigh  out  three  portions  of  the  fine 
borings  of  one  assay  ton  (29.167  grams)  each,  and  assay  each 
separately.  Place  each  sample  in  a  750  c.c.  lipped  beaker  and 
cover  with  a  watch-glass.  Treat  the  sample  with  10  c.c.  of 
mercuric  nitrate  (or  25  c.c.  of  the  saturated  acid  sulphate 
described  in  17,  Chapter  III).  Rotate  the  beaker  until  the 
copper  is  thoroughly  amalgamated,  then  add  90  to  100  c.c.  of 
sulphuric  acid  (d.,  1.84),  placing  the  beaker  on  a  hot  plate  .or 
burner,  and  boil  until  the  copper  is  dissolved  to  a  paste. 
Converter  drillings  require  about  twenty  minutes,  refined  metal 
one  half-hour.  Remove  the  beaker  and  allow  it  to  cool  to  a 
semi-liquid  sludge.  When  cool,  add  about  500  c.c.  of  hot  water, 
stir  until  the  copper  sulphate  dissolves,  then  add  4  to  6  c.c.  of 
salt  solution  (1  c.c.  equals  50  mg.  of  silver),  or  an  equivalent 
amount  of  hydrochloric  acid.  Stir  well  and  filter  at  once  (or 
within  fifteen  minutes)  through  a  triple  15  cm.  filter,  or  a  7  cm. 
S.  &  S.  598  doubled  filter.  Wash  out  the  beaker  with  hot  water, 
1  S.  N.  Scott,  Jr.,  Mines  and  Minerals,  1910. 


168  ANALYSIS  OF  COPPER 

then  wipe  the  inside  with  filter  paper,  and  add  the  pieces  to  the 
filter.  Thorough  washing  of  the  filter  itself  is  not  necessary. 

Transfer  the  wet  filter  and  contents  to  a  2.5  inch  scorifier  in 
the  bottom  of  which  is  a  piece  of  sheet  lead  about  2  inches 
(5  cm.)  square.  Some  operators  omit  the  lead  foil,  but  instead, 
give  the  scorifiers  a  preliminary  glaze  with  pure  melted  litharge 
to  prevent  the  silver  from  sticking  to  the  bottom.  Burn  off  the 
paper  at  a  low  heat,  best  in  a  closed  oven  heated  to  nearly 
350°  C.  This  chars  the  paper  slowly  below  the  melting  point  of 
silver  chloride,  and  therefore  without  any  danger  of  loss  of  silver. 
The  author  obtains  a  better  reduction  by  dusting  2  grams  of 
powdered  lead  on  the  inside  of  the  paper  before  incineration. 
When  the  paper  is  entirely  consumed,  add  30  grams  of  test  lead 
and  scorify,  pour  at  the  right  time  to  obtain  a  12  to  15  gram 
lead  button,  and  cupel  the  lead.  The  cupel  should  show  good 
"  feat  hers."  It  should  be  made  of  60-mesh  bone-ash  and  of 
medium  hardness.  The  writer  prefers  the  Brownite  cupel,  which 
absorbs  less  silver  in  the  direct  cupellation  of  silver  chloride. 

Part  the  gold  as  in  method  (1),  and  subtract  the  weight  of 
the  gold  from  that  of  the  original  bead,  the  difference  being  the 
silver.  Greenwood  insists  that  the  bead  must  be  inquarted 
with  additional  silver  if  the  silver  is  lower  than  five  times  the 
gold.  The  two  results  on  gold  should  check  within  .02  ounce 
per  ton  and  the  silver  within  1  per  cent  of  its  own  weight. 
The  average  of  the  two  results  for  each  metal  to  be  reported. 
If  platinum  exists  in  the  copper,  separate  it  from  gold  by  one 
of  the  special  methods  (9  and  10,  Chapter  VIII). 

Limits  of  Accuracy.1  —  The  mercury  salt  is  added  to  promote 
solution  and  prevent  formation  of  sulphide  of  copper.  None  of 
the  silver  is  carried  into  solution  unless  the  heating  is  too  long 
continued  after  the  copper  is  dissolved,  or  unless  the  silver  is 
more  than  60  to  70  ounces  per  ton  of  copper.  In  these  cases, 
a  small  amount  of  silver  is  apt  .to  be  dissolved,  but  even  in  copper 
containing  up  to  150  ounces  per  ton,  the  silver  results  on  such 
metal  will  be  fairly  comparable  with  those  of  the  nitric  acid 
method,  although,  on  the  whole,  averaging  a  little  lower. 

If  the  silver  is  much  in  excess  of  50  ounces  per  ton,  even  the 
addition  of  salt  solution  will  not  precipitate  absolutely  all  of  the 
silver.  The  gold  results  agree  closely  with  those  of  the  quarter 
1  Communicated  by  A.  M.  Smoot. 


THE  ELECTROLYTIC  REFINERY  169 

assay  ton  all-fire  method  on  most  coppers  (which  can  be  sampled 
correctly  with  as  low  a  quantify  as  .25  assay  ton).  Some  very 
impure  material  —  especially  ft  it  contains  much  arsenic, 
antimony,  selenium,  and  tellurium  —  may  yield  results  a  little 
lower  than  by  the  dry  method. 

With  such  impure  copper,  better  results  will  be  obtained  by 
melting  the  silver  precipitate  in  a  10-gram  crucible  with  a  flux 
used  in  western  reduction  works  and  recommended  first  by 
Scott.  Burn  the  papers  at  a  low  heat  and  flux  with  15  grams 
sodium  carbonate,  7.5  grams  potassium  carbonate,  1.5  grams 
borax  glass,  1.5  grams  silica,  1.5  grams  flour,  30  grams 
litharge.  Place  the  crucible  in  a  muffle  or  pot  at  a  low  heat 
and  finish  at  a  high  heat,  —  -  time,  twenty  to  twenty-five 
minutes. 

4.  Method  with  Potassium  Bisulphate  and  Sulphuric  Acid.  - 
This  assay  is  based  on  another  scheme  for  the  solution  of  the 
copper   without   loss   of    gold.       It   has   the   single    advantage 
in  certain  cases,  that  the  solution  may  be  subsequently  employed 
for  the  estimation   of  arsenic   and  nickel,   or  zinc.     Place  one 
assay  ton  of  very  fine  borings  in  a  750  c.c.  lipped  beaker,  add  30 
grams  of  potassium  bisulphate  crystals  and  100  c.c.  of  sulphuric 
acid  (d.,  1.84).     Boil  for  half  an  hour,  so  rapidly  that  the  foam 
half  fills  the   beaker.     When  the  foam  lessens  and   the  metal 
appears  to  be  dissolved,  grasp  the  beaker  with  a  holder  made 
from  a  piece  of  harness  strap  (1  inch  by  12  inches),  and  whirl  it 
until  any  black  sulphide  is  washed  down  from  the  sides.     Boil 
for  ten  minutes  to  destroy  the  black  sulphide,  then  proceed  as 
in  the  mercury  method,   melting  the  residue  with  the  crucible 
flux. 

If  a  trace  of  copper  still  remains  undissolved,  transfer  it  to 
a  No.  3a  casserole  and  boil  it  with  3  grams  of  bisulphate  and 
10  c.c.  of  acid.  There  is  a  tendency  for  insoluble  sulphide  to 
remain  also,  and  the  boiling  must  be  carefully  watched.  Owing 
to  the  small  amount  of  sulphide  precipitated  with  the  silver,  the 
reduction  of  silver  in  very  rich  material  should  be  more  com- 
plete than  in  the  previous  method. 

5.  Nitric  Acid  Method  for  Silver  in  Metallic  Copper.  —  As 
nitric  acid  has  a  slight  solvent  action  on  gold,  this  assay  is  only 
depended  upon  for  the  silver  contents.1 

1  Modification  of  A.  M.  Smoot  and  F.  D.  Greenwood. 


170  ANALYSIS  OF  COPPER 

Weigh  out  two  portions  of  copper  borings  of  one  assay  ton 
each  and  place  them  in  750  c.c.  lipped  beakers.  Add  100  c.c. 
of  water  and  90  to  100  c.c.  of  nitric  acid  (d.,  1.42).  The  acid 
may  be  added  in  small  portions  of  30  c.c.  each  at  intervals  of 
about  one  hour,  if  the  gold  is  to  be  determined  this  way.  Other- 
wise, add  the  acid  in  portions  of  50  c.c.  If  gold  is  present, 
precipitate  a  small  amount  of  silver  chloride  with  standard  salt 
solution  in  order  to  collect  the  gold,  then  filter  through  double 
filter  papers  when  settled,  and  wash  the  papers  free  from  copper. 
(One  may  filter  the  solution  from  gold  without  the  collector  of 
silver  chloride.)  The  beaker  is  finally  wiped  with  paper,  adding 
this  to  the  filter.  Transfer  the  gold  precipitate  to  a  Bartlett 
shape  scorifier,  which  contains  a  lining  of  sheet  lead,  or  has  been 
glazed  on  the  inside  with  molten  litharge.  To  the  filtrate,  add  a 
calculated  amount  of  sodium  chloride  solution  as  in  former 
methods,  but  avoiding  much  excess.  Stir  well,  and  allow  to 
stand  several  hours,  better,  over  night.  If  the  silver  present  is 
less  than  50  mg.  (50  ounces  per  ton),  the  silver  chloride  is  apt 
to  remain  too  finely  divided. 

Some  operators  add  5  c.c.  of  sulphuric  acid  followed  by  3  c.c. 
of  a  saturated  solution  of  lead  acetate  and  stir  briskly  for  several 
minutes,  allowing  to  settle  as  usual  before  filtering.  It  is, 
however,  better  to  avoid  the  use  of  a  collector  if  possible.  When 
the  silver  only  is  required,  the  precipitating  reagent  may  be 
added  to  400  c.c.  of  water  in  a  separate  beaker,  and  poured 
quickly  into  the  hot  syrupy  nitrate  of  copper,  avoiding  the  sides 
of  the  beaker.  The  solution  is  then  heated  rapidly  on  the  hot 
plate  and  boiled  one  minute,  with  the  result  that  the  silver  is 
clotted  sufficiently  to  filter  clear  after  settling.  When  the 
supernatant  liquid  is  quite  clear,  filter  through  double  filters, 
or  a  598  S.  &  S.  7  cm.  filter  supported  on  a  platinum  cone 
with  coarse  perforations.  Wash  the  beaker,  wipe  it  with  filter 
paper  or  a  large  camel's  hair  pencil,  and  heat  the  last 
washings  to  boiling  before  filtration.  Wash  the  papers  free 
from  copper  salt,  transfer  all  filters  to  the  scorifier  containing 
the  gold. 

Five  grams  of  powdered  test  lead  may  be  sprinkled  inside 
the  silver  filter  (Greenwood).  Dry  and  ignite  the  papers  very 
carefully  at  a  low  heat,  best  in  a  closed  oven  heated  to  a  temper- 
ature which  will  cause  the  paper  to  char  without  flaming,  or 


THE  ELECTROLYTIC  REFINERY  171 

about  300°  C.  As  silver  chloride,  melts  at  a  temperature  one 
hundred  degrees  higher  than  ledd,  there  will  be  no  loss  of  silver 
below  the  point  at  which^the  leacPmelts  down. 

On  removing  the  scorifier  to  the  open  air,  the  carbon  will 
glow  gently  until  consumed.  Add  25  to  35  grams  of  test  lead 
to  the  ash  with  .5  gram  of  borax,  and  scorify  at  a  low  heat  just 
long  enough  so  that  the  resultant  button  shall  weigh  12  to  15 
grams.  The  button  should  then  be  cupeled  at  a  low  heat  so 
that  the  feather  litharge  completely  surrounds  the  bead.  The 
cupel  should  be  made  of  bone-ash  ground  to  pass  a  60-mesh 
sieve  and  should  be  of  medium  hardness. 

Part  the  weighed  beads  of  gold  and  silver  as  in  the  previous 
methods.  Pour  off  the  first  (1  : 5)  acid,  wash  once  with  distilled 
water,  and  then  place  the  tube  in  a  beaker  of  water  and  boil  for 
half  an  hour  with  nitric  acid  (d.,  1.30)  (Smoot),  or  possibly  with 
acid  (d.,  1.42)  as  recommended  by  Greenwood.  Pour  off  the 
strong  acid  and  wash  three  times  with  distilled  water.  Place 
the  gold  in  a  porcelain  crucible,  dry,  anneal,  and  weigh  as  usual, 
taking  the  silver  by  difference.  If  the  gold  is  more  than  one- 
fifth  of  the  silver,  the  bead  must  be  inquarted.  The  two  results 
on  gold  should  check  within  .02  ounce  per  ton  and  the  silver 
within  .5  per  cent  of  the  amount  present,  taking  the  average  of 
two  results  in  each  case. 

6.  Rapid  Assay ;  Direct  Cupellation  of  Silver  Chloride.1  - 
Trie  product  of  most  of  the  Lake  Superior  refineries  is  tested  by 
direct  cupellation.  The  loss  due  to  scorification  is  nearly  elimi- 
nated. Higher  results  with  this  process  are  obtained  by  using 
Brownite  cupels,  in  which  the  lime  and  magnesia  have  a  reducing 
effect  on  silver  chloride  not  possessed  by  bone-ash. 

Dissolve  about  29  grams,  or  1  A.  T.,  of  drillings  in  a  750  c.c. 
beaker  with  150  c.c.  of  nitric  acid  (d.,  1.42),  added  in  three 
portions  of  50  c.c.  The  beaker  is  placed  on  the  hot  plate,  the 
red  fumes  boiled  out,  and  the  beaker  immediately  removed. 
The  requisite  amount  of  salt,  or  hydrochloric  acid  to  provide  a 
slight  excess,  is  placed  on  the  bottom  of  a  500  c.c.  beaker  and 
covered  by  400  c.c.  of  water.  The  water  is  now  poured  quickly 
into  the  hot  copper  solution,  without  touching  the  sides  of  the 
container.  Boil  for  one  minute,  cool,  and  settle  over  night. 
Filter  on  a  598  S.  &  S.  7  cm.  paper,  supported  by  a  coarsely 
1  Trans.  A.  I.  M.  E.  31,  484. 


172  ANALYSIS  OF  COPPER 

perforated  platinum  cone.  Wash,  filter,  etc.,  as  in  the  preceding 
method. 

Cupellation.  —  Dust  the  inside  of  the  moist  filter  with  1.5 
grams  of  30-mesh  lead.  Store  the  filters  in  a  funnel  rack  until 
the  muffle  is  ready,  then  fold  each  one  before  charring,  and  place 
it,  point  down,  in  a  1.25  inch  (3.2  cm.)  Brownite  cupel.  These 
give  higher  results  than  bone-ash  as  already  explained.  The 
charring  should  be  done  in  a  separate  muffle  at  very  low  red 
heat.  The  empty  cupels  should  be  placed  in  the  hottest  muffle 
for  half  an  hour  before  use,  and  then  brought  down  to  the 
temperature  of  the  cooler  muffle  before  charring  the  filters.  A 
very  little  lead  is  placed  under  the  paper,  also. 

When  a  gray  ash  remains,  add  4.5  to  5  grams  of  lead,  transfer 
to  the  hottest  muffle,  melt  down  quickly,  bring  forward  and 
finish  in  a  single  row  at  a  low  heat.  At  the  same  time,  another 
set  is  being  charred  in  the  cooler  muffle. 

The  beads  must  be  pushed  back  into  the  hottest  part  of  the 
muffle  about  15  seconds  before  the  "blick,"  to  remove  the  last 
trace  of  lead  when  using  this  make  of  cupel.  One  operator  uses 
potassium  bromide  as  a  precipitant,  but  the  actual  loss  of  silver 
due  to  the  solubility  of  the  chloride,  alone,  is  only  .1  to  .12  Troy 
ounce  per  ton  of  copper. 

If  a  corrected  assay  is  required,  silver  chloride  from  weighed 
foil  may  be  cupeled  as  proofs,  or  the  average  cupel  correction 
may  be  determined  for  a  month's  run  of  assays  of  uniform 
material,  by  crushing  and  assaying  all  the  Brownite  cupels  used 
during  that  time. 

THE  ELECTROLYTIC  ASSAY   OF   CRUDE   COPPER 

In  the  assay  of  refined  metal  (Chapter  XI),  5  grams  of  drill- 
ing are  directly  dissolved  in  a  standard  acid  mixture,  and  the 
whole  electrolyzed.  In  order,  however,  to  obtain  an  average 
sample  of  crude  metal  such  as  slabs  or  anodes,  it  is  necessary  to 
derive  the  final  assay  weight  by  riffling  down  a  large  sample  to 
80  grams,  or  to  two  portions  of  40  grams  each.  These  portions 
are  weighed,  dissolved,  and  an  aliquot  portion  of  the  diluted 
solution  electrolyzed. 

Aliquoting  Apparatus,  —  Automatic  Pipettes.  —  In  Chapter  I, 
the  most  suitable  types  of  stands,  flasks,  and  pipettes  are 
described.  The  manner  of  mounting  the  Smoot  " wash-out" 


THE  ELECTROLYTIC  REFINERY 


173 


pipette  is  illustrated  by  its  designer  in  Fig.  13.  The  water- 
jacketed  type  is  fully  described  in  a  paper  by  W.  C.  Ferguson.1 
Each  has  its  advocates,  J3ut  the  'writer  prefers  the  former,  which 
is  not  so  elaborate.  In  mounting,  it  is  best  to  have  the  filter 
pump  connected  with  a  large  vacuum  reservoir  fitted  with  a 
mercury  trap  which  maintains  a  vacuum  equivalent  to  about  3 
inches,  or  75  mm.,  of  mercury.  This  pressure  is  sufficient  to 
work  the  apparatus  rapidly. 
The  vacuum  reservoir  should 
be  connected  to  a  large  bottle 
for  holding  waste  liquid,  which 
is  drawn  over  in  filling  and 
washing  the  pipette;  —  this  is 
shown  in  the  cut,  directly  be- 
hind the  support.  The  sides 
of  the  delivery  tube  are  paral- 
lel instead  of  tapering  to  a 
small  orifice.  This  facilitates 
rapid  filling  and  delivery  and 
also  gives  a  sharp  cut-off  at 
the  end  when  the  pipette  is 
full;  that  is,  the  solution  is 
exactly  parallel  with  the 
bottom  of  the  glass  tube,  and 
there  are  no  air  bubbles  which 
sometimes  occur  when  the 
lower  end  is  constricted.  Re- 
peated measurements  are 
practically  identical,  provided 


Fig.  13.  —  Smoot  Automatic  Pipette. 


that  the  temperature  of  the 
liquid  does  not  vary. 

Standardizing.  —  For  aliquoting  solutions  of  copper,  liter 
flasks  and  50  c.c.  pipettes  are  the  most  convenient  volumes,  the 
unit  size  being  the  Mohr  liter,  true  liter,  or  any  similar  volume. 
The  important  point  is  that  the  pipette  shall  hold  an  exact 
fraction  of  the  contents  of  the  flask;  —  in  this  case,  one-twentieth. 
It  is  impossible  to  obtain  apparatus  sufficiently  accurate  from 
the  makers,  and  the  chemist  should  standardize  his  own.  Pipettes 
may  be  ordered  to  hold  rather  more  (say  about  .1  c.c.)  than  one- 
1  J.  Ind.  and  Eng.  Chem.  2  (1910),  187. 


174  ANALYSIS  OF  COPPER 

twentieth  of  the  volume  of  the  flasks.  The  number  of  liter 
flasks  required  will  depend  on  the  amount  of  work  to  be  done 
per  day,  but  two  pipettes  will  be  sufficient  for  any  number  of 
flasks,  the  second  pipette  being  held  in  reserve. 

Clean  and  dry  all  the  flasks  and  select  any  one  of  them  as  a 
standard.  Counterpoise  it  on  a  balance  which  has  capacity  of 
2000  grams  and  a  sensibility  of  at  least  .02  gram.  Fill  the 
standard  flask  with  water  at  room  temperature  exactly  to  the 
mark,  and  then  counterpoise  "the  added  water  by  pouring  test 
lead  into  a  bottle  placed  on  the  other  pan.  The  bottle  of  test 
lead  then  represents  the  weight  of  the  water.  Remove  every- 
thing from  the  balance  and  counterpoise  another  empty  flask; 
replace  the  bottle  of  test  lead  and  add  water  at  room  tempera- 
ture to  the  empty  flask  until  it  balances  with  the  bottle  of  lead. 
Make  any  necessary  changes  in  the  mark  to  bring  the  capacity 
of  the  second  flask  to  that  of  the  first.  By  proceeding  in  this 
way  with  all  the  flasks,  they  may  be  made  to  have  exactly  the 
same  capacity  as  the  first  standard  flask,  and  this  is  accom- 
plished without  any  errors  that  might  be  due  to  inequalities  in 
the  balance  beam,  or  errors  due  to  temperature,  provided  that 
the  water  remains  at  a  uniform  temperature.  Any  trace  of 
water  on  the  inside  of  necks  must  be  removed  before  the  final 
balancing. 

The  graduation  of  the  pipette  to  the  flask  is  best  done  by 
working  on  pure  copper.  To  this  end,  a  standard  copper  of 
known  copper  and  silver  content  should  be  taken.  Selected 
wire  bar  turnings  with  a  content  of  99.95  per  cent  make  the  best 
standard.  The  exact  content  should  be  ascertained  by  making  a 
number  of  assays  by  the  "five  gram"  method  of  Chapter  XI. 
Then  weigh  40  grams  of  the  standard  copper  into  the  standard 
liter  flask  and  dissolve  it  in  a  mixture  of  200  c.c.  of  water,  120 
c.c.  of  nitric  acid  (d.,  1.42),  and  20  c.c.  of  sulphuric  acid  (d.,  1.84), 
adding  the  nitric  in  two  portions  of  60  c.c.  Boil  the  liquid,  cool 
to  room  temperature,  and  dilute  to  about  950  c.c.  Mix  the  liquid 
by  rotating  the  flask,  and  test  with  a  thermometer  graduated 
in  fifths  of  a  degree  C.,  to  be  sure  that  the  temperature  is  nor- 
mal. Dilute  to  the  mark  and  mix  thoroughly  by  stopping  the 
neck  of  the  flask  with  a  well-fitting  rubber  stopper,  inverting 
and  shaking  several  times,  and  testing  the  temperature  again 
after  mixing.  Have  the  pipette  mounted  in  a  place  free  from 


THE  ELECTROLYTIC  REFINERY  175 

draughts  where  the  thermometer  does  not  vary  more  than  1°  C. 
As  there  is  always  a  differerice  between  the  upper  and  lower 
parts  of  a  room,  the  flasks  shoved  be  kept  near  the  level  of  the 
pipette,  which  is  connected  to  the  filter  pump  as  illustrated. 

Pour  about  300  c.c.  of  the  copper  solution  into  a  No.  3  beaker 
and  fill  the  pipette  by  placing  the  stem  in  the  beaker  and  turn- 
ing the  stop  cock  so  that  the  right-hand  bore  connects  with  the 
waste  bottle  and  the  filter  pump  with  the  bulb,  and  fill  the 
pipette,  letting  a  little  liquid  run  over  into  the  waste  bottle.  Re- 
move the  beaker  and  turn  the  stop  cock  so  that  the  funnel  open- 
ing connects  with  the  bulb,  running  the  liquid  to  waste.  Repeat 
this  operation,  thus  washing  the  pipette  twice  with  copper  solu- 
tion. Fill  the  pipette  a  third  time  in  the  same  way  and  make 
sure  that  no  air  bubbles  appear  in  the  stem  immediately  below 
the  stop  cock.  Remove  any  solution  adhering  to  the  outside 
of  the  stem  with  a  piece  of  soft  paper,  being  careful  not  to  touch 
the  opening  in  the  stem  with  the  paper.  Run  the  solution  into 
an  electrolytic  beaker,  and  wash  the  pipette  with  three  succes- 
sive portions  of  water  of  10  c.c.  each  introduced  through  the 
funnel,  letting  the  wash  water  run  into  the  main  liquid.  Make 
three  or  four  aliquots  in  this  way  and  determine  the  copper  in 
each  electrolytically,  just  as  with  the  standard  copper,  making 
the  necessary  additions  of  water  and  acid  to  secure  the  best 
conditions. 

If  the  pipette  was  made  a  little  too  large,  as  it  should  have 
been,  the  copper  obtained  will  weigh  more  than  one-twentieth 
of  the  amount  weighed  into  the  standard  flask,  but  three  or  four 
assays  made  in  this  way  should  not  vary  more  than  .0003  gram 
between  the  maximum  and  minimum  weight.  Determine  the 
capacity  of  the  pipette  per  running  centimeter.  This  may  be 
done  either  by  using  standard  copper  solution  and  making  several 
estimations  of  copper,  contained  in  the  liquid  measured  from  a 
small  mark  scratched  on  the  stem  near  the  bulb  to  the  end  of 
the  stem;  or  it  may  be  done  by  weighing  some  water  into  a 
small  flask,  filling  the  stem  from  this  flask  to  a  mark  and  weigh- 
ing the  flask  again,  taking  the  weight  of  the  water  by  dif- 
ference, and  calculating  the  volume.  Calculate  the  number  of 
cubic  centimeters  that  must  be  cut  from  the  lower  end  of  the 
stem  to  reduce  the  holding  capacity  of  the  pipette  to -the  re- 
quired volume,  and  by  means  of  a  sharp  file  cut  off  about  two 


176  ANALYSIS  OF  COPPER 

millimeters  less  than  the  required  length.  Grind  the  edges  of 
the  tip  square  by  rubbing  the  end  against  emery  cloth  stretched 
on  a  plane  surface  and  redetermine  the  capacity  of  the  pipette 
in  relation  to  the  standard  flask  by  standard  copper,  as  before. 
The  pipette  should  now  hold  very  slightly  more  than  one- 
twentieth  of  the  volume  of  the  flask.  A  little  judgment  will 
show  how  much  more  should  be  taken  from  the  stem  to  bring 
the  capacity  exactly  right,  and  this  small  amount  should  be 
removed  by  grinding  with  emery. 

Finally,  the  accuracy  of  the  pipette  should  be  tested  by 
aliquoting  from  several  40-gram  portions  of  standard  copper 
dissolved  in  the  same  flask  as  before.  All  the  tests  should  agree 
within  .02  per  cent.  The  question  of  temperature  is  very  im- 
portant in  this  work  and  all  the  operations,  in  which  it  could 
affect  the  results,  should  be  checked  with  a  thermometer.  The 
pipette  may  be  water-jacketed  if  desired  (like  the  instrument 
devised  by  Ferguson),  but  this  precaution  is  hardly  necessary 
since  a  variation  of  1°  C.,  or  even  more,  in  the  room  temperature 
does  not  perceptibly  affect  that  of  the  solutions  within  the  time 
required  for  mixing  and  aliquoting.  Several  of  the  other  flasks 
should  be  checked  against  the  pipette  in  the  same  way  and  one 
or  two  of  them  set  aside  as  standards,  so  that  future  purchases 
of  flasks  may  be  standardized  easily  to  the  pipette.  The  second 
pipette  should  be  standardized  like  the  first  and  held  in  reserve 
in  case  of  breakage. 

At  any  time,  the  capacity  of  any  flask  may  be  checked  against 
the  pipette  by  means  of  the  standard  copper,  and  it  is  well  to 
run  at  least  one  standard  a  week  to  make  sure  that  no  change 
occurs  in  the  relative  capacities.  The  pipette  should  be  cleaned 
daily  by  filling  it  with  strong  sulphuric  acid  saturated  with 
potassium  bichromate,  and  a  very  little  vaseline  may  be  used 
as  a  lubricant  for  the  stopcock. 

THE  ASSAY  OF  CRUDE  COPPER  BY  ELECTROLYSIS 

7.  Converter  Slabs  and  Blister.  —  A.  M.  Smoot  and  F.  D. 
Greenwood  describe  the  same  methods  and  use  the  same 
pipettes,  and  the  procedure  of  the  majority  of  refineries  is  based 
on  a  scheme  similar  to  the  one  to  be  described.  This  modifica- 
tion is  intended  for  99  per  cent  metal  which  does  not  contain  a 
proportion  of  impurities  which  would  be  sufficient  to  interfere 


THE  ELECTROLYTIC  REFINERY  111 

with  the  direct  electrolysis  of  the,  original  solution  of  the  sample. 
The  sample  should  be  ground*  to  pass  at  least  a  tV-inch  sieve 
(Chapter  II),  and  that  part  of  fhe  borings  which  is  finer  than 
60-mesh  should  contain  at  least  95  per  cent  of  copper;  that  is, 
the  sample  should  be  quite  homogeneous.  For  heterogeneous,  or 
variable  metal,  method  8  should  be  used. 

Divide  the  sample  repeatedly  on  a  split  sampler  .having 
quarter-inch  (63  mm.)  divisions  until  two  portions  of  about  40 
grams  each  are  obtained  by  a  coarse  balance.  The  division 
should  be  made  within  about  .5  gram  of  the  required  weight  so 
that  only  a  small  amount  need  be  added  to,  or  taken  from, 
the  sample  to  bring  the  weight  to  exactly  40  grams.  In  this 
division,  loss  of  dust  must  be  avoided  and  great  care  must  be 
used  to  mix  the  sample  after  each  division  so  that  coarse  and  fine 
parts  will  be  cut  out  in  equal  proportion. 

Adjust  the  weight  on  an  analytical  balance  to  exactly  40 
grams  by  a  spatula  and  transfer  to  a  liter  flask.  Add  200  c.c.  of 
water,  60  c.c.  of  nitric  acid  (d.,  1.42),  20  c.c.  of  sulphuric  acid 
(d.,  1.84);  when  the  action  has  subsided  add  60  c.c.  more  of 
nitric  acid,  and  sufficient  sodium  chloride  solution  to  precipitate 
all  the  silver  present.  Thus,  in  copper  containing  about  80 
ounces  of  silver  per  ton,  an  amount  of  sodium  chloride  equivalent 
to  100  ounces  of  silver  may  be  safely  added  or  6.5  c.c.  of  N/5 
sodium  chloride. 

Set  the  flask  in  a  warm  place  until  the  copper  is  dissolved, 
then  boil  the  liquid  until  the  red  fumes  are  expelled,  cool  to 
room  temperature,  dilute  to  about  925  c.c.,  mix  the  liquid  well 
by  rotation  without  spattering,  again  test  the  temperature,  and 
finally  adjust  the  volume  exactly  to  the  mark.  Now  close  the 
flask  with  a  rubber  stopper  and  mix  by  inverting  and  shaking 
several  times.  Filter  a  portion  of  the  liquid  rapidly  through  an 
18  cm.  folded  filter  (S.  &  S.  588)  into  a  clean  dry  beaker.  Reject 
the  first  100  c.c.  of  filtrate  and  from  the  next  300  to  400  c.c. 
take  50  c.c.  (or  2  grams  of  sample)  by  means  of  the  pipette 
described  above.  Add  to  this  portion,  2  c.c.  of  a  mixture  of 
equal  parts  of  nitric  acid  (1.42)  and  sulphuric  acid  (1.84),  dilute 
to  130  c.c.,  and  deposit  the  copper  on  perforated  platinum  cyl- 
inders, using  .35  ampere  for  about  eighteen  hours. 

The  electrolytic  beaker  should  be  covered  during  the  time  of 
deposition  with  a  closely  fitting  split  watch  glass,  which  is 


178  ANALYSIS  OF  COPPER 

washed  down  with  a  fine  stream  of  water  after  sixteen  hours. 
If  the  assay  is  nearly  finished,  the  newly  immersed  surface  of  the 
cathode  will  remain  quite  bright,  but  if  more  copper  is  present 
than  can  be  deposited  in  two  hours,  the  stem  will  be  discolored 
in  about  half  an  hour.  This  serves  well  enough  as  a  practical 
guide,  but  the  electrolyte  should  finally  be  tested  with  hydrogen 
sulphide  after  the  electrodes  have  been  withdrawn.  Disconnect 
the  cathode  very  rapidly,  substituting  a  beaker  of  water,  or 
plunging  the  cathode  under  water,  rinse  several  times,  drain 
over  blotting  paper,  rinse  it  with  alcohol,  drain  again,  and  dry 
over  a  Bunsen  flame,  being  careful  not  to  use  sufficient  heat  to 
oxidize  the  deposit.  Cool  and  weigh  the  copper. 

In  testing  the  electrolyte  with  hydrogen  sulphide,  an  experi- 
enced eye  can  usually  detect  .0002  gram  of  copper,  even  in  the 
presence  of  some  arsenic  and  antimony.  Any  weighable  deposit 
should  be  filtered  off,  calcined,  dissolved  in  nitric  acid,  and  the 
copper  estimated  by  the  color  test  if  desired,  though  this  extra 
work  is  rarely  necessary.  Duplicates  made  in  separate  flasks 
from  the  beginning,  should  check  within  .05  per  cent;  duplicates 
taken  from  the  same  flask,  within  .01  per  cent  or  .02  per  cent. 

This  method  does  not  include  insoluble  copper  which  is  rarely 
found  in  converter  bars.  (Each  brand  of  copper  should  be  tested 
as  some  nickeliferous  copper  leaves  a  residue  from  nitric  acid 
solution  consisting  of  oxides  of  nickel  and  iron.)  In  such  a  case, 
the  sample  should  be  dissolved  in  a  large  beaker,  the  liquid  filtered 
into  the  liter  flask,  and  the  ignited  residue  fused  with  a  little 
potassium  bisulphate  in  a  porcelain  crucible,  adding  the  water 
solution  of  the  melt  to  the  flask. 

It  will  be  observed  that  no  account  is  taken  of  the  volume  of 
the  insoluble  residue,  or  of  the  silver  chloride  in  the  liter  flask. 
Usually,  these  are  too  small  to  be  considered,  since  bar  copper 
rarely  contains  more  than  .10  per  cent  of  insoluble  matter,  nor 
would  silver  chloride  equivalent  to  100  ounces  per  ton  appre- 
ciably affect  the  liquid  volume. 

F.  D.  Greenwood  makes  no  allowance  for  the  volume  of  the 
silver  salt  unless  the  silver  runs  over  600  ounces  per  ton.  The 
possible  evaporation  of  the  liquid  during  filtration  is  a  source 
of  error,  but  many  experiments  by  Smoot  and  Greenwood  have 
shown  that  it  is  negligible  if  the  filter  is  kept  full  and  the  work 
is  done  rapidly. 


THE  ELECTROLYTIC  REFINERY  179 

8.  Non-homogeneous  Metal,  r—  When  wide  differences  exist 
between  the   coarse  and  fine  parts  of  the  ground    sample,    as 
when   much    cuprous   oxide   from    overblown    copper  is  present 
or    when    the    metal    contains   considerable    nickel,  the  method 
of   direct   splitting    should   not   be   employed    (see    preparation 
of    samples) .    In   such   cases,  the   whole  ground   sample   should 
be  weighed   and  sifted  through   a  40-mesh  screen   (see   copper 
sampling,  Chapter  II) .      The  final  samples  should  consist  of  accu- 
rately weighed  portions  of  the  "coarse"   and  " fines,"  and  the 
40-gram    charges    should    be   made    by   weighing   proportionate 
parts   of    each;    otherwise    the    procedure   is    the    same    as   in 
modification  7. 

9.  Low-grade    Bars,    By-products,    Leady    Mattes,    etc.  — 
In   these    products,   the   bars   contain  excessive  impurity  which 
interferes    with    direct    electrolysis.      According   to    Smoot    and 
Greenwood,  either  of  the  foregoing  modifications  may  be  em- 
ployed for  obtaining  the  weighed  sample,  depending  on  the  char- 
acter of  the  borings. 

Method.  —  Dissolve  forty  grams  of  the  sample,  contained  in  a 
large  beaker  or  flask,  in  a  mixture  of  200  c.c.  of  water  and  120  c.c. 
of  the  strong  nitric  acid,  adding  the  latter  in  two  portions  of  60 
c.c.  each.  Greenwood  also  adds  20  c.c.  of  sulphuric  acid.  Pre- 
cipitate the  silver  as  usual,  and  boil  vigorously,  filter  into  a 
flask,  and  wash  the  residue  well  with  hot  water  so  that  all  solu- 
ble copper  is  obtained  in  the  flask.  Remove  the  flask  and  wash 
the  residue  with  hot  sodium  thiosulphate  to  dissolve  silver 
chloride. 

Wash  the  residue  again  with  water,  dry,  ignite,  and  fuse  it  in 
a  porcelain  crucible  with  potassium  bisulphate  at  least  one-half 
an  hour  to  dissolve  nickel.  Dissolve  the  fusion  in  water,  add  a 
very  little  sodium  chloride  to  remove  any  silver  that  may  have 
escaped  solution  in  the  sodium  thiosulphate,  then  boil  and  filter 
into  the  main  solution.  Cool  to  room  temperature,  make  up  to 
volume,  and  take  out  50  c.c.  for  test. 

A.  M.  Smoot  adds  at  this  point  a  pure  solution  of  ferric 
nitrate  containing  sufficient  iron  to  retain  all  arsenic,  antimony, 
selenium,  or  tellurium,  .2  gram  usually  being  required.  Make 
the  liquid  alkaline  with  excess  of  ammonia,  stir  well,  and  allow 
the  mass  to  settle  on  a  steam  bath  for  half  an  hour.  Filter  and 
wash  the  residue  with  dilute  ammonia.  The  greater  part  of  the 


180  ANALYSIS  OF  COPPER 

copper  is  in  the  solution;  set  it  aside,  or,  if  the  volume  is  too 
large,  reduce  it  by  rapid  evaporation. 

Dissolve  the  ferric  hydroxide  in  hot  dilute  hydrochloric  acid, 
nearly  neutralize  with  ammonia,  leaving  it,  however,  slightly  acid, 
add  40  c.c.  of  a  saturated  water  solution  of  sulphur  dioxide,  and 
set  the  liquid  in  a  warm  place  for  half  an  hour  until  the  iron  is 
reduced  to  a  ferrous  condition.  Then  add  2  c.c.  of  a  15  per  cent 
solution  of  potassium  thiocyanate  (150  grams  per  liter). 

Allow  the  cuprous  salt  to  settle  for  half  an  hour  in  a  warm 
place,  filter  through  a  doubled  9  cm.  paper,  and  wash  the  salt 
once  with  warm  water,  containing  2  per  cent  of  ammonium 
nitrate.  Transfer  the  filter  to  a  No.  2  porcelain  crucible,  dry 
slowly,  and  ignite  gently  in  a  muffle,  beginning  at  a  very  low 
temperature.  After  the  paper  is  burned,  raise  the  heat  gradually 
until  the  carbon  is  all  consumed,  then  cool,  add  3  c.c.  of  water 
and  6  c.c.  of  nitric  acid.  Set  the  crucible  on  a  steam  bath  until 
the  copper  oxide  is  all  dissolved  and  the  solution  is  clear.  Boil 
for  a  few  minutes,  and  add  the  liquid  to  the  main  solution. 

Acidify  the  liquid,  if  necessary,  by  adding  (1:1)  sulphuric 
acid  until  it  is  faintly  acid,  then  add  6  c.c.  of  strong  nitric,  ad- 
just the  volume  to  130  to  180  c.c.,  and  electrolyze  as  in  modifica- 
tion 7. 

NOTE.  —  Nickeliferous  residues  may  be  dissolved  by  boiling 
with  10  c.c.  of  sulphuric  acid,  5  c.c.  of  nitric,  and  3  grams  of 
potassium  bi sulphate.  Dilute,  heat  to  boiling,  filter,  and  add 
filtrate  to  main  solution.  It  is  better  to  omit  the  ferric  nitrate 
if  possible  from  assays  of  nickeliferous  copper.  Add  more  acids 
before  electrolysis. 

10.  Assay  of  Crude  Copper  Containing  Selenium  or  Tellu- 
rium. —  If  much  tellurium  is  present  it  would  contaminate  the 
copper,  and  the  method  may  be  modified  as  follows  : 

Proceed  with  the  blister,  or  converter,  drillings  as  in  method 
9  until  the  hydrochloric  acid  solution  of  the  ferric  hydroxide 
has  been  obtained.  To  the  iron  solution  add  about  one  gram 
of  tartaric  acid  in  solution,  then  add  sodium  hydroxide  until 
the  liquid  is  faintly  alkaline.  Pass  a  rapid  current  of  hydrogen 
sulphide  which  will  precipitate  copper  and  iron  as  sulphides  but 
retain  arsenic,  antimony,  selenium,  and  tellurium  in  solution. 
Filter  on  a  12  cm.  paper  and  wash  once  or  twice  with  a  2  per 


THE  ELECTROLYTIC  REFINERY  181 

cent  solution  of  sodium  sulphide  free  from  polysulphides.  Trans- 
fer the  mass  back  into  the  beaker  by  means  of  a  fine  jet  from  a 
wash  bottle,  and  add  J.O  c.c.  &  hydrochloric  acid  (d.,  1.20), 
which  will  dissolve  the  ferrous  sulphide  but  leave  the  copper. 
Dilute  the  solution  with  100  c.c.  of  hydrogen  sulphide  water  to 
make  sure  that  all  the  copper  is  precipitated,  stir  well,  and  filter 
through  the  same  12  cm.  paper  that  held  the  sulphides  originally. 
Wash  the  copper  sulphide  with  water,  transfer  the  paper  and 
contents  to  a  large  porcelain  crucible,  dry,  and  ignite  at  a  low 
temperature  until  the  carbon  is  burned  off.  Dissolve  the  mixed 
copper  oxide  and  sulphide  in  dilute  nitric  acid  and  proceed  as  in  9. 

NOTE.  —  In  the  absence  of  much  bismuth,  one  may  employ 
the  more  rapid  method  of  the  author,  described  in  the  assay 
of  refined  copper  (Chapter  XI).  This  is  simply  a  direct  pre- 
cipitation of  the  selenium  and  tellurium  from  a  sulphuric  acid 
solution  of  the  sample  with  sulphur  dioxide,  omitting  the  pre- 
cipitation with  ferric  hydroxide,  but  using  sufficient  acids  in  the 
final  electrolyte  to  hold  up  the  arsenic  and  antimony  present. 

11.  Separation  of  Copper  as  Thiocyanate.  —  This  method  is 
included  as  an  alternative.  The  separation  of  impurities,  except 
tellurium,  is  quite  complete,  but  the  operation  is  tedious. 

Proceed  as  in  modification  9  until  the  final  50  c.c.  portion 
is  obtained  in  a  500  c.c.  beaker.  Make  this  strongly  alkaline 
with  ammonia,  adding  the  reagent  until  the  copper  hydroxide 
redissolves,  then  make  acid  with  hydrochloric,  adding  about  2 
c.c.  in  excess.  Now  add  50  c.c.  of  saturated  sulphur  dioxide 
solution,  dilute  to  300  c.c.,  and  then  add  at  once  20  c.c.  of 
potassium  thiocyanate  (15  per  cent  solution),  stir  well,  and  let 
the  mixture  stand  on  a  bath  at  80°  C.  for  an  hour  and  a  half, 
or  until  the  mass  settles,  leaving  a  clear  liquid  above.  Filter  on 
doubled  filters,  using  a  15  cm.  paper  inside  and  a  12.5  cm.  paper 
outside,  wash  with  a  warm  2  per  cent  solution  of  ammonium 
nitrate,  transfer  the  filter  and  contents  to  a  large  porcelain  or 
fused  silica  crucible,  dry  slowly  in  a  muffle,  and  ignite  as  in  pre- 
vious methods.  Dissolve  in  nitric  acid. 

F.  D.  Greenwood  modifies  the  method  of  Smoot  by  taking 
one-twentieth  of  a  20-gram  sample  to  avoid  the  treatment  of  a 
large  bulk. 

Dissolve  a  20-gram  sample  in  10  c.c.  water,  60  c.c.  of  nitric 


182  ANALYSIS  OF  COPPER 

acid,  and  10  c.c.  of  sulphuric  acid,  add  sodium  chloride  to  remove 
all  silver,  and  boil  to  expel  red  fumes.  Then  dilute  to  mark  and 
draw  out  one-twentieth,  equal  to  1  gram  of  copper.  Evaporate 
to  fumes,  dilute  to  200  c.c.,  neutralize  with  ammonia,  make 
slightly  acid  with  sulphuric  acid  (or  hydrochloric  in  presence  of 
arsenic).  Pass  sulphur  dioxide  gas  through  the  boiling  solution 
until  all  the  iron  and  copper  have  been  reduced. 

In  four  or  five  minutes,  the  copper  may  be  thrown  down  as 
thiocyanate,  but  pass  the  gas  until  the  mass  is  perfectly  white. 
Boil  and  settle  until  clear,  then  filter  and  wash.  Dissolve  with 
nitric  acid,  evaporate  to  fumes  with  10  c.c.  of  sulphuric  acid, 
dilute,  transfer  to  a  tall  beaker,  add  4  c.c.  of  ammonia  and  5  c.c. 
of  nitric  acid,  and  electrolyze  over  night. 

12.  Purification  of  Cathode  by  Second  Electrolysis.  —  This 
simple  means  of  purification  may  be  used  to  obtain  a  final  pure 
weighable  copper  deposit  in  cases  where  the  interfering  impuri- 
ties are  arsenic  and  antimony,  only.  The  first  cathode  deposit 
is  placed,  without  weighing,  in  another  electrolytic  beaker,  cov- 
ered with  water  and  40  c.c.  of  acid  mixture  (see  Chapter  XI), 
and  the  electrolysis  repeated  as  soon  as  the  copper  is  dissolved. 
The  beaker  is  carefully  covered  with  a  watch  glass  perforated 
with  a  small  hole  just  large  enough  to  pass  the  stem  of  the 
electrode. 

FOREIGN  METALS  IN  CRUDE  COPPER 

Nickel  must  be  estimated  frequently  in  crude  material.'  This 
element  may  be  recovered  from  the  electrolyte  remaining  from 
the  electrolysis  of  copper.  The  wash  waters  and  test  portions 
should  be  saved  and  the  combined  solutions  evaporated  to  fumes 
with  10  c.c.  of  sulphuric  acid.  The  diluted  solution  is  then  made 
strongly  ammoniacal  and  electrolyzed  as  directed  in  Chapter  VII, 
method  2. 

Cobalt  and  zinc  deposit  with  the  nickel.  They  may  be 
separated  from  the  nickel,  either  before,  or  after,  electrolysis  by 
methods  4  and  5,  Chapter  VII. 

To  avoid  repetition,  the  determination  of  all  other  impurities 
in  crude  metal  will  be  included  with  the  analysis  of  refined 
copper  in  Chapters  XII  and  XIII.  The  only  essential  difference 
in  tests  of  crude  metal  is  the  reduction  of  sample  weights  from 
50  or  100  to  a  limit  of  2  to  20  grams,  and  the  occasional 
necessity  for  examination  of  insoluble  residues. 


•m 

PART  III 

CHAPTER  XI 

THE  ELECTROLYTIC  ASSAY  OF  REFINED  COPPER 
THE  DETERMINATION  OF  COPPER 

The  Electrolytic  Assay  of  High-grade  Copper.  —  The  first 
requirement  of  an  exact  technical  method  is  that  the  sample 
shall  be  small  enough  to  permit  direct  electrolysis  without  divi- 
sion by  pipettes,  but  large  enough,  however,  to  neutralize  the 
errors  of  manipulation  and  thus  permit  duplicate  tests  to  check 
within  the  limit  of  .015  per  cent.  Recently,  the  Alloys  Com- 
mittee of  the  American  Chemical  Society  has  recommended 
the  5-gram  assay  as  a  standard  with  this  limitation  of  accuracy. 

The  second  requirement  is  that  an  assay  started  at  the  close 
of  business  must  finish  about  noon  of  the  next  day.  The  acids 
and  water  should  be  strictly  free  from  chlorides.  It  is  much 
safer  to  complete  the  washing  of  electrolytic  beakers  by  rinsing 
them  with  distilled  water,  and  placing  them  on  wooden  pegs  to 
drain,  than  to  attempt  to  dry  them  with  cloths. 

When  refined  copper  is  treated  with  dilute  acids,  some  im- 
purities may  remain  insoluble  (as  noted  in  9,  Chapter  X,  and  in 
the  first  page  of  the  next  chapter),  but  not  usually  in  sufficient 
amount  to  enclose  any  copper. 

Elements  Determined.  —  In  tests  of  refined  metal,  it  is  cus- 
tomary to  deposit  and  report  the  silver  with  the  copper.  This 
works  well  up  to  a  limit  of  .3  per  cent  of  silver,  or  100  ounces 
per  ton.1  The  methods  in  general  use  in  the  United  States  are, 
First,  the  exact  10-gram  assay;  Second,  the  standard  5:gram 
assay  for  routine  work;  Third,  the  rapid  assay  with  some  rotary 
device. 

1.  The  Ten-gram  Assay.  —  According  to  this  modification, 
devised  by  F.  Andrews,  ten  grams  of  drillings  of  cast  copper 
are  weighed  into  a  tall  lipless  beaker  of  500  c.c.  capacity  and 

i  Keller;  Heath. 


184 


ANALYSIS  OF  COPPER 


dissolved  in  50  c.c.  of  water  and  35  c.c.  of  nitric  acid  (d.,  1.42). 
When  solution  is  complete,  the  glasses  and  beaker  are  carefully 
washed  down  and  the  solution  evaporated  until  all  the  free  acid 
is  driven  off  and  the  crystallizing  point  reached.  After  cooling, 
add  100  c.c.  of  water,  10  c.c.  of  ammonia  (d.,  .91),  then  6  c.c.  of 
sulphuric  acid  (d.,  1.84),  and  make  the  solution  up  to  275  to 
300  c.c.  Make  the  deposition  on  a  platinum  cylinder  which 

may  be  2.25  inches  (5.7  cm.)  in 
height  and  1.6  inches  (4.1  cm.)  in 
diameter,  of  about  15  grams  weight, 
and  perforated  with  24  holes  to  the 
linear  inch  (1  per  mm.)  —  Fig.  14. 
Keller1  recommends  about  seven 
.5  mm.  holes  to  the  inch  (25  mm.). 
Use  a  current  of  1  ampere  per 
assay  from  the  lighting  circuit.  In 
the  morning,  after  fifteen  hours, 
wash  down  the  split  watch  glasses 
and  sides  of  the  beaker,  and  watch 
the  clean  cathode  stem,  thus  ex- 
posed to  the  liquid,  for  one-half 
hour.  If  no  copper  is  deposited, 
withdraw  1  c.c.  of  solution  and  test 
it  on  a  spot  plate  with  hydrogen 
sulphide  water.  The  copper  is 
generally  deposited  in  sixteen  hours, 
only  the  slightest  gassing  is  ever 
observed  at  the  cathode,  and  no 


Wire   Frame  Anode 


Assembly 
Fig.  14.  —  Special  Electrodes. 


impurity  has  ever  been  found  by  Andrews  in  the  deposited 
copper. 

The  experience  of  the  author  shows  that  it  is  easier  to  dis- 
solve the  copper  in  70  c.c.  of  the  acid  mixture  given  in  the 
" five-gram  method"  and,  since  a  trace  of  copper  is  always  re- 
tained in  the  electrolyte,  it  is  more  accurate  to  cut  the  volume 
of  electrolyte  down  to  about  175  c.c. 

Other  precautions  in  manipulation  are  described  in  the  next 
methods. 

2.  The  Standard  Five-gram  Electrolytic  Assay.  —  This  de- 
scription follows  closely  a  report  of  the  Alloys  Committee  of  the 
1  Bull.  80,  A.  I.  M.  E.,  1913,  2093. 


THE  ELECTROLYTIC  ASSAY  OF  REFINED  COPPER      185 

American  Chemical  Society  on  a  standard  method  for  the  bat- 
tery assay  of  copper.  The  author1  proposed  a  standard  acid 
mixture  for  dissolving  copper,  which  should  permit  direct  elec- 
trolysis without  evaporation,  and  should  provide  a  sufficient 
excess  of  sulphuric  acid  to  hold  back  the  impurities  until  the 
assay  is  finished,  notwithstanding  the  reduction  of  much  of  the 
nitric  acid  to  ammonia  by  the  electric  current. 

General  Instructions.  —  Six  ingots,  or  other  castings,  are 
selected  at  random  from  a  lot  and  drilled  through,  without 
oxides,  as  directed  in  Chapter  II.  Weights  should  be  calibrated 
and  frequently  re-checked.  It  is  recommended 2  to  use  a  special 
5-gram  brass  weight  in  weighing  the  samples  and  to  have  the 
weight  of  sample  always  within  5  mg.  of  5  grams.  When  the 
cathode  with  its  deposit  is  finally  weighed,  the  identical  weights 
are  to  be  used  with  which  the  cylinder  was  tared,  plus  the  special 
5-gram  brass  weight.  This  brings  all  the  change  or  deficiency 
in  the  final  weight  on  a  small  fractional  weight  and  the  beam 
and  rider. 

Electrodes.  —  The  cathode  is  a  platinum  sheet  of  5  by  10 
cm.  giving  a  depositing  surface,  counting  both  sides,  of  100  sq. 
cm.  This  sheet  is  formed  into  a  cylinder  of  the  open  type, 
and  the  stem  is  riveted  and  soldered  with  gold  to  the  middle  of 
the  sheet.  There  should  be  no  seam  which  cannot  be  cleaned 
completely  by  two  washings.  The  anode  is  made  from  1-mm. 
platinum  wire,  formed  into  a  spiral  of  seven  turns  having  a 
diameter  of  12.5  mm.  and  a  height  of  38  mm.,  the  stem  being 
straight  and  125  mm.  long. 

Electrolytic  and  Low- Resistance  Lake  Copper.  —  This  modifica- 
tion is  adapted  to  the  grades  of  copper  covered  by  the  specifica- 
tions of  the  American  Society  for  Testing  Materials  as  given  in 
its  Year  Book  for  1913,  pages  241-247.  The  silver  is  deposited 
with  the  copper  as  in  1,  and  is  included  as  such;  when  it  is 
desired  to  correct  for  the  silver  this  is  determined  in  a  larger 
separate  sample  and  the  amount  found  is  deducted  from  the 
total  cathode  deposit.  The  deposition  of  the  copper  with  the 
silver  is  said  to  work  well  up  to  the  limit  of  .3  per  cent  silver  or 
100  ounces  per  ton.  All  assays  are  to  be  made  in  duplicate  within 
an  outside  limit  of  .015  per  cent. 

1  J.  Ind.  and  Eng.  Chem.  3,  74.     Trans.  A.  I.  M.  E.  27,  390. 

2  Greenwood,  personal  communication. 


186  ANALYSIS  OF  COPPER 

Electrolysis.  —  Place  5  grams  of  the  clean  bright  drillings  in 
a  tall  lipless  beaker  which  is  provided  with  a  well-fitting  cover 
glass  and  add  a  mixture  of  7  c.c.  of  nitric  acid  (d.,  1.42),  10  c.c. 
of  sulphuric  acid  (d.,  1.84),  and  25  c.c.  of  water.  This  mixture 
is  used  as  a  stock  " Assay  Solution,"  42  c.c.  being  measured  for 
each  5-gram  sample.  The  electrolysis  beakers  are  from  100  to 
125  mm.  tall  and  55  mm.  in  diameter  across  the  bottom,  with 
a  total  capacity  of  225  to  300  c.c.  After  the  assays  have  stood 
for  a  few  minutes,  and  the  action  has  nearly  ceased,  place  them 
on  a  steam  bath  having  a  temperature  of  90°  to  100°  C.  and  allow 
them  to  remain  there  until  solution  is  completed  and  the  red  fumes 
have  disappeared.  Wash  the  cover  and  the  sides  of  the  beaker, 
dilute  the  solution  to  130  to  150  c.c.  and  electrolyze. 

NOTE.  —  (Use  of  the  dilute  solution  above  described  prevents 
a  violent  reaction  and  a  consequent  loss  of  copper  in  spray  or 
vapors.  This  solution  should  not  be  boiled,  since  this  likewise 
may  cause  a  loss  of  copper.) 

During  electrolysis  the  beakers  are  covered  with  two  pairs  of 
split  watch  glasses  placed  at  right  angles  with  each  other.  The  cur- 
rent in  each  solution  should  be  .95  to  one  ampere,  that  is  1  ampere 
per  square  decimeter,  which  will  require  6  to  10  volts  if  the  assays 
are  arranged  in  parallel.  (The  current  may  also  be  taken  from 
a  110-volt  circuit  through  incandescent  lamps  or  rheostats  as 
regulators.)  It  is  convenient  to  start  the  assays  at  night;  after 
about  fifteen  hours  wash  the  cover  glasses,  electrodes,  and  beakers 
and  reduce  the  current  to  .5  or  .6  ampere  per  solution.  As 
soon  as  the  cathodes  begin  to  evolve  gas,  reduce  the  current  to 
.4  ampere  per  solution.  At  this  time  (or  as  soon  as  the  assay  is 
thought  to  be  finished),  take  out  about  1  c.c.  of  liquid,  place  it 
in  a  depression  in  a  porcelain  test  plate,  and  add  2  or  3  drops  of 
fresh  hydrogen  sulphide  water.  If  the  slightest  discoloration 
occurs,  continue  the  electrolysis,  repeating  the  test  until  there  is 
no  discoloration  whatever.  If  possible  the  assay  should  finish 
without  decided  evolution  of  gas. 

Without  interrupting  the  current,  siphon  off  the  acid  solution, 
at  the  same  time  filling  the  beakers  with  distilled  water.  Re- 
move the  cathodes  quickly,  rinse  them  in  distilled  water  and  two 
successive  baths  of  alcohol.  (Redistilled  "pyro,"  or  denatured, 
alcohol  gives  satisfactory  results  at  much  less  expense  than  pure 


THE  ELECTROLYTIC  ASSAY  OF  REFINED  COPPER      187 

ethyl  alcohol.)  An  experienced  operator  can  quickly  remove  a 
cathode  (with  one  motion)  and  immerse  it  in  water  without  loss. 
Throw  off  the  excess  alcokol  by  a^quick  motion  of  the  hand  and 
ignite  the  remainder  by  bringing  the  cathode  quickly  to  the  flame 
of  an  alcohol  lamp  (or  gasolene  burner) ;  then  keep  the  cathode 
moving  continually  as  the  alcohol  burns.  This  method  of  burning 
off  dries  the  cathode  without  causing  oxidation,  whereas  drying 
in  an  oven  at  100°  C.  generally  causes  an  increase  in  weight. 

NOTE  1.  —  It  has  been  shown1  that  a  few  thousandths  of  a 
per  cent  of  copper  may  remain  in  solution  without  being  detected 
by  the  hydrogen  sulphide  test  on  the  spot  plate.  This  amount 
of  copper  is  negligible  in  many  instances,  but  when  necessary 
to  make  exact  determinations,  as  in  the  complete  analysis  of 
copper,  make  the  solution  from  the  electrolysis  slightly  alkaline, 
neutralize  with  hydrochloric  acid  (d.,  1.19),  adding  3  c.c.  excess, 
evaporate  to  50  c.c.,  and  precipitate  with  hydrogen  sulphide. 
Filter  off  the  copper  sulphide,  treat  with  nitric  and  sulphuric 
acids,  and  deposit  the  small  amount  of  copper  from  this  solu- 
tion by  electrolysis  and  add  it  to  that  obtained  in  the  original 
determination. 

NOTE  2.  —  By  the  use  of  rotating  anodes,  gauze  or  perforated 
electrodes,  or  the  Frary  solenoid,  it  is  possible  to  use  a  high 
current  density  and  to  reduce  the  time  required  for  depositing 
the  copper  to  four,  or 'even  two  and  a  half,  hours.  Good  results 
can  be  obtained  by  experienced  workers,  but  there  is  much  more 
chance  for  error.  The  slow  or  overnight  method,  which  is  more 
certain  and  which  requires  less  of  the  operator's  time,  is,  there- 
fore, recommended.  (A  trace  of  platinum  is  carried  over  to 
the  cathode  in  warm  solutions.  It  may  be  removed  by  redis- 
solving  the  weighed  deposit  in  dilute  "solution."  Current  in 
solenoid  =  4  to  4.5  amperes.)  Perfect  assays  may  be  obtained 
by  keeping  each  beaker  cold.  (See  Fig.  lOb,  Chapter  I.) 

2b.  Modification  for  Low-grade  or  Casting  Copper.  —  For  all 

grades  of  copper  which  are  not  included  in  the  specifications  of 
the  American  Society  for  Testing  Materials,  as  electrolytic  and 
low-resistance  Lake  copper,  the  procedures  given  below  are  recom- 
mended. These  brands  may  contain  a  considerable  amount  of 
arsenic  and  some  antimony,  tellurium,  bismuth,  and  nickel.  All 
1  Heath,  J.  Ind.  and  Eng.  Chem.  4,  404  (1912). 


188  ,  ANALYSIS  OF  COPPER 

assays  are  made  in  duplicate  and  must  check  within  an  outside 
limit  of  .015  per  cent. 

With  solutions  of  such  coppers  the  use  of  about  2  c.c.  of  an 
addition  agent  prepared  by  boiling  "hard  oil"  with  strong  nitric 
acid,  cooling,  and  removing  the  grease  has  been  recommended.1 
This,  it  is  said,  will  permit  the  use  of  high-current  densities 
and  yet  allow  the  copper  to  be  deposited  pure  and  bright. 
Moreover,  it  is  said  that  arsenic  and  antimony,  when  present,  do 
not  contaminate  the  copper.  It  seems  probable,2  however,  that 
copper  deposited  from  such  solutions  is  not  quite  pure  and  that 
it  is  more  accurate  to  purify  the  cathode  deposit  (modification 
I  below)  or  to  give  a  preliminary  treatment  to  the  solution 
(modification  II). 

The  committee  gives  preference  to  II,  and  I  should  be  used 
only  in  the  presence  of  small  amounts  of  impurities. 

Modification  I.  —  Carry  out  the  assay  exactly  as  given  for 
electrolytic  and  low-resistance  Lake  copper.  Place  the  cathode 
in  a  clean  beaker,  cover  with  a  watch  glass  perforated  with  a 
small  hole,  just  large  enough  to  accommodate  the  stem  of  the 
electrode,  add  42  c.c.  of  stock  " assay  solution"  and  water 
enough  to  cover  the  sheet.  Let  it  stand  upon  the  steam  bath 
until  the  coating  is  dissolved.  Re-electrolyze  in  the  regular 
manner. 

Modification  II?  —  Dissolve  the  5-gram  sample  in  42  c.c. 
of  the  "assay  solution"  and  evaporate  until  all  the  nitric  acid 
is  expelled.  Redissolve  in  70  c.c.  of  water  and  add  3  c.c.  ferric 
nitrate  solution  (1  c.c.  =  .01  gram  iron).  Transfer  the  solution 
to  a  lipped  beaker  and  place  the  original  beaker  under  a  funnel 
fitted  with  $  small  filter  paper.  Precipitate  the  iron  from  the 
hot  liquid  by  ammonia,  filter,  and  wash  out  salts.  Place  the 
solution  on  a  hot  plate  to  concentrate,  reprecipitate  the  hydrox- 
ide from  dilute  sulphuric  acid  in  a  very  small  volume  of  solu- 
tion, and  add  the  filtrate  to  the  main  solution.  Reprecipitate  the 
hydroxide  once  more  from  dilute  sulphuric  acid,  filter,  wash 
thoroughly,  and  add  the  filtrate  to  the  main  solution.  Make 
acid  with  dilute  sulphuric  acid  and  add  2  to  3  c.c.  of  nitric  acid 
(d.,  1.42).  Deposit  the  copper  as  in  the  method  for  electrolytic 
and  low-resistance  lake  copper. 

1  Guess,  Trans.  A.  I.  M.  E.  36,  605  (1905). 

2  Keller,  Ibid.  Bull.  80,  2099  (1913);  Heath,  /.  Ind.  Eng.  Chem.  3,  75. 
•  Heath  (Senter  modified),  J.  Am.  Chem.  Soc.  26,  1123  (1904). 


THE  ELECTROLYTIC  ASSAY  OF  REFINED  COPPER   189 

Modification  III.1 — (For  copper  containing  only  traces  of 
antimony  or  bismuth  but  sufficient  selenium  or  tellurium  to 
interfere.)  » 

Dissolve  the  5-gram  sample  in  40  c.c.  of  *" assay  solution" 
and  evaporate  until  fumes  appear,  or  until  the  residue  is  white. 
Redissolve  in  60  c.c.  of  water  and  saturate  the  boiling  solu- 
tion for  ten  minutes  with  sulphur  dioxide  gas,  removing  the 
solution  from  the  lamp  when  the  gas  is  started.  The  gas  may 
be  generated  by  dropping  cold  saturated  sodium  sulphite  solution 
into  strong  sulphuric  acid.  It  is  also  conveniently  obtainable 
in  cylinders.  Let  the  precipitate  settle  for  a  few  hours,  filter, 
and  wash  with  a  little  hot  water.  Boil  the  filtrate  gently  to 
remove  most  of  the  sulphur  dioxide  gas.  Ignite  the  filter  in 
a  porcelain  crucible  to  volatilize  the  selenium  and  tellurium, 
redissolve  the  oxidized  residue  in  1.5  to  2  c.c.  of  nitric  acid 
and  add  to  the  main  solution.  Deposit  the  copper  as  in  the 
method  for  electrolytic  and  pure  lake  copper. 

NOTE.  —  The  selenium  is  said  to  be  carried  down  by  sul- 
phur dioxide  as  a  selenide  of  silver,  but  the  roasting  sufficiently 
removes  the  elements  selenium  and  tellurium.  When  silver  is 
to  be  removed,  the  selenium,  etc.,  are  thrown  down  with  the 
silver  by  the  sulphur  dioxide  gas  and  the  precipitation  is  then 
completed  by  the  addition  of  chlorides  or  hydrochloric  acid. 

Modification  IV.  —  (For  copper  high  in  arsenic  only.2)  The 
committee  gives  preference  to  B. 

A.  —  Dissolve  the  sample  in  40  to  42  c.c.  of  the  "assay  solu- 
tion" in  the  regular  way  and  add  5  grams  of  ammonium  nitrate. 
Electrolyze  as  usual. 

B.  —  Dissolve  the  sample  in  60  to  66  c.c.  of  the  "assay  solu- 
tion" instead  of  40  c.c.    Electrolyze  in  the  usual  manner. 

3.  Notes  on  the  Manipulation  of  the  Frary  Solenoid.  — 
This  rotary  device  of  Professor  F.  C.  Frary 3  produces  rotation  of 
the  electrolyte  in  the  tall  assay  beaker  by  the  action  of  a  mag- 
netic field.  The  apparatus  has  been  described  and  illustrated  in 
Chapter  I. 

1  Heath,  J.  Am.  Chem.  Soc.  26, 1123  (1914);  Keller,  Trans.  A.  I.  M.  E., 
Bull.  80,  2098  (1913). 

2  Heath,  J.  Am.  Chem.  Soc.  26,  1124;  /.  Ind.  and  Eng.  Chem.  3, 75  (1911). 

3  /.  Am.  Chem.  Soc.  17,  395;  Z.  Elektrochem.  23,  358. 


190  ANALYSIS  OF  COPPER 

This  apparatus  makes  it  possible  to  obtain  results  in  three 
hours,  or  even  less,  if  a  circulation  of  cold  water  is  introduced  be- 
tween the  beaker  and  copper  cylinder.  There  are  two  objections 
to  rapid  deposition  of  copper  which  have  been  alluded  to  :  —  the 
liability  to  slight  oxidation  unless  the  cathode  is  withdrawn 
within  five  minutes  after  the  deposition  of  copper  is  complete; 
second,  a  trace  of  platinum  is  carried  over  from  the  anode 
in  warm  solutions.  It  may  be  removed,  as  already  directed, 
by  filtering  the  solution  of  the  cathode  deposit  through  paper 
and  igniting  the  platinum  residue,  which  may  amount  to  .005 
per  cent.  The  amount  of  " assay  solution"  should  not  exceed 
50  c.c.  if  the  solution  is  allowed  to  heat.  A  perfect  assay  may 
always  be  obtained  with  50  c.c.  of  " assay  solution"  if  the 
electrolyte  is  kept  very  cold  by  water  circulation.  With  5  grams 
of  copper,  the  current  may  be  raised  to  4  or  4.5  amperes.  In 
about  two  hours,  or  just  as  soon  as  the  liquid  becomes  colorless, 
wash  down  the  covers  and  beaker,  and  twenty  minutes  later  begin 
to  make  tests  once  in  five  minutes  upon  test  portions  of  1  c.c. 
of  the  electrolyte.  As  soon  as  a  negative  test  is  obtained,  with- 
draw the  cathode  very  rapidly  with  one  motion  and  plunge  it 
into  a  beaker  of  cold  water.  Wash,  ignite,  and  weigh  as  usual. 
The  perforated  cathode  of  Andrews  and  Keller  (method  1) 
should  be  employed. 

In  the  case  of  casting  copper,  if  the  first  deposit  is  slightly 
impure,  it  may  be  redissolved  in  diluted  stock  solution  and  re- 
plated.  The  use  of  50  c.c.,  or  more,  of  " assay  solution"  will 
prevent  sponginess  and  no  platinum  will  be  dissolved,  if  the 
electrolyte  is  kept  very  cold  as  recommended. 


CHAPTER  XII 

THE    DETERMINATION    OF   FOREIGN   ELEMENTS   IN    COPPER 

Division  of  Work.  —  Metallurgical  chemists  usually  consider 
that  it  is  more  rapid  and  accurate  to  make  special  determina- 
tions of  single  elements  or  groups  upon  separate  portions  of 
copper  drillings  from  the  same  casting.  In  addition  to  the 
electrolytic  assays  described  in  Chapter  XI,  it  is  customary  to 
weigh  out  a  second  sample  of  50  grams  for  electrolysis  followed 
by  separation  of  iron,  nickel,  cobalt,  and  zinc;  also  a  third 
sample  of  25  to  100  grams  for  the  separation  of  the  arsenic  or 
selenium  groups  of  metals.  A  fourth  sample  weight  of  20  grams 
is  taken  for  sulphur  and  lead  determinations;  occasionally  a 
fifth  for  -a  check  on  bismuth,  and  a  sixth  of  50  grams  for  the 
estimation  of  oxygen.  It  is  reasonably  correct  to  determine  the 
known  impurities  in  commercial  copper,  subtract  their  sum  from 
100  per  cent,  and  take  the  difference  as  oxygen.  A  sample  for 
oxygen  test  should  be  weighed  out  from  the  same  bottle  of 
drillings  as  the  sample  for  battery  assay,  because  the  oxygen 
increases  nearly  as  much  as  the  copper  decreases.  A  single  cast- 
ing shows  much  segregation  in  this  respect. 

As  it  is  occasionally  necessary  to  examine  a  small  piece  of 
metal,  two  general  schemes  are  presented  in  methods  1,  2,  3,  4, 
and  5,1  by  which  most  of  the  impurities  are  removed  from  a 
single  solution.  Although  adapted  to  some  routine  work,,  these 
older  methods  (1,  2,  4,  5),  which  are  modifications  of  the  original 
process  of  Dr.  W.  Hampe,2  are  not  so  accurate  for  the  estimation 
of  minute  amounts  as  the  special  methods  which  follow  them. 

1.  Foreign  Metals  (with  Separation  of  Copper  as  Thiocya- 
nate).3 — Transfer  50  grams  of  pure  copper  or  25  grams  of  " cast- 
ing" copper  to  a  750  c.c.  beaker.  Twenty-five  grams  of  metal 
require  for  solution  125  c.c.  distilled  water,  35  to  40  c.c.  pure  sul- 

1  /.  Am.  Chem.  Soc.  29,  699;   27,  317. 

2  Z.  Berg.    Hutten  and  Salinen-Wesen  21,  218;  22,  93;   also  Fresenius' 
Zeitsch.  1874. 

3  J.  Am.  Chem.  Soc.  16,  785. 


192  ANALYSIS  OF  COPPER 

phuric  acid  (d.,  1.84),  and  28  to  30  c.c.  of  nitric  acid  (d.,  1.42). 
For  a  50-gram  sample  double  the  reagents  but  add  the  nitric 
acid  in  three  portions.  Dissolve  by  heating,  dilute  with  an 
equal  volume  of  water,  heat  to  40°  C.,  and  pass  sulphur  dioxide 
until  the  liquid  is  saturated  with  the  gas.  If  an  accurate  separa- 
tion of  selenium  or  tellurium  is  required,  the  original  solution 
should  be  evaporated  to  dryness  to  remove  all  nitric  acid,  before 
dilution  and  reduction  with  sulphur  dioxide.  One  or  two  drops 
of  hydrochloric  acid  may  be  added  to  complete  the  deposition 
of  the  silver.  After  standing  over  night  in  a  warm  place  (below 
40°  C.),  pour  off  the  supernatant  liquid  through  a  small  filter 
into  a  calibrated  2-liter  flask.  The  sediment,  after  washing  out 
the  last  trace  of  copper,  may  contain  gold,  silver  as  metal  and 
chloride,  selenium,  tellurium,  possibly  also  lead  sulphate  and 
traces  of  antimony  and  bismuth. 

Dilute  to  one  liter  or  more  and  remove  the  copper  by  adding 
gradually  a  standard  solution  of  ammonium  (or  potassium) 
thiocyanate,  while  a  current  of  sulphur  dioxide  is  conducted  into 
the  bottom  of  the  flask  through  a  long  tube  or  pipette.  Give 
the  flask  a  vigorous  rotation  before  each  addition  of  reagent 
until  the  precipitate  changes  to  the  white  salt.  A  sufficient 
amount  of  copper  should  finally  remain  to  impart  a  faint  tint 
to  the  solution.  Withdraw  the  delivery  tube,  fill  the  flask  with 
water  to  the  mark,  and  mix  the  contents  thoroughly  by  pouring 
several  times  into  a  large  dry  beaker.  Allow  the  mass  to  settle, 
filter  off  a  known  portion,  say  1800  to  1900  c.c.  for  analysis, 
and  expel  the  sulphur  dioxide  by  heating.  It  is  necessary  to 
allow  for  the  volume  of  the  thiocyanate,  the  specific  gravity  of 
which  is  nearly  three  (Hampe).  Twenty-five  grams  of  copper  give 
48  grams  of  the  salt,  hence  the  volume  of  the  salt  is  16  c.c.  and 
the  volume  of  the  solution  in  the  flask  at  the  filling  mark  is  not 
2000  but  1984  c.c.  Similarly,  the  volume  of  the  solution  from 
a  50-gram  sample  is  1968  c.c.  The  determination  of  iron  by 
this  method  is  not  very  certain  on  account  of  the  variable  trace 
of  iron  in  the  large  amount  of  thiocyanate  required. 

Analysis  of  Insoluble  Residue.  —  Remove  the  residue  as  com- 
pletely as  possible  from  the  filter  and  destroy  the  latter  by 
repeated  gentle  evaporation  with  a  little  red  fuming  nitric  acid 
in  a  small  porcelain  casserole.  Add  the  residue  and  treat  again 
with  nitric  acid  until  completely  oxidized.  After  the  acid  is 


DETERMINATION  OF  FOREIGN  ELEMENTS  IN  COPPER    193 

finally  removed  by  evaporation  gn  the  steam  bath,  digest  the 
dried  residue  with  dilute  hydrochloric  acid,  which  leaves  the 
silver  chloride  undissolve^.  If  a  ifrace  of  antimony  is  suspected, 
digest  the  silver  chloride  with  20  c.c.  of  a  saturated  solution  of 
yellow  ammonium  sulphide,  containing  .5  gram  of  ammonium 
chloride,  in  order  to  dissolve  the  antimony.  Preserve  this 
extract  and  afterwards  unite  it  with  the  remainder  of  the 
antimony  obtained  from  the  main  solution.  Oxidize  the  sul- 
phides with  nitric  acid,  evaporate  to  dry  ness,  add  dilute  hydro- 
chloric acid  in  sufficient  amount  to  dissolve  the  salts  and 
separate  the  silver;  then  filter.  If  silver  alone  is  required, 
it  is  possible  to  char  and  oxidize  the  sulphides  direct  upon  a 
Brownite  cupel,  cover  with  powdered  lead,  and  finish  the  cupella- 
tion.  If  silver  chloride  is  to  be  weighed,  it  is  best  to  filter  it 
upon  a  dried  asbestos  felt  in  a  Gooch  crucible,  and  dry  at 
150°  C. 

Precipitate  the  selenium  and  tellurium  in  the  acid  filtrate 
from  the  silver  chloride  by  sulphur  dioxide  in  excess.  If  a 
separation  of  the  two  elements  is  required,  evaporate  the  solution 
to  10  c.c.  or  to  5  c.c.  if  possible,  and  then  add  strong  hydro- 
chloric acid  (d.,  1.2),  until  the  acid  is  90  per  cent  strength.  Heat 
nearly  to  boiling  to  reduce  selenium,  charge  with  sulphur  dioxide 
until  cold,  and  allow  to  settle. 

Filter  off  the  selenium  upon  an  asbestos  felt  which  has  been 
washed  in  strong  acid  and  water,  dried,  and  weighed.  Then  pro- 
ceed to  wash,  dry,  and  weigh  the  selenium.  Separate  the  tellurium 
in  the  filtrate  according  to  special  method  16,  Chapter  XIII. 
Lead  is  also  determined  by  a  special  electrolytic  method,  given 
in  the  next  chapter.  Hydroxyl  amine  will  throw  down  selenium 
but  has  little  effect  on  tellurium. 

Analysis  of  the  Main  Solution.  —  Expel  the  sulphur  dioxide 
by  heat,  then  charge  the  solution  with  hydrogen  sulphide  until 
saturated,  to  precipitate  the  arsenic  group  of  metals  and  the 
remaining  traces  of  copper.  Extract  the  arsenic,  antimony,  and 
tin  by  digestion  of  the  sulphides  with  sodium  (or  potassium) 
sulphide  as  directed  in  4.  Charge  the  original  solution  with 
hydrogen  sulphide  again,  and  filter  to  prove  that  the  first  pre- 
cipitation was  complete.  Repeat  the  treatment  if  more  than  a 
trace  of  sulphide  appears  after  all  sulphur  has  been  extracted 
with  ethyl  alcohol  and  carbon  bisulphide. 


194  ANALYSIS  OF  COPPER 

Owing  to  the  presence  of  an  excessive  quantity  of  salts,  the 
iron,  nickel,  and  zinc  are  subsequently  removed  from  the  main 
solution  by  rendering  the  liquid  slightly  alkaline  with  ammonia 
and  recharging  with  hydrogen  sulphide.  Filter  off  the  sulphides, 
and  repeat  the  process  as  often  as  necessary.  Dissolve  the 
sulphides  by  heating  with  dilute  hydrochloric  acid,  adding  a 
little  nitric  acid,  if  much  nickel  and  cobalt  are  present.  Pre- 
cipitate the  iron  twice  with  ammonia  from  the  oxidized  solution. 
If  a  trace  of  manganese  is  present,  add  some  bromine  water 
during  the  first  precipitation.  When  the  iron  is  to  be  purified 
a  second  time,  the  manganese  may  be  taken  out  of  the  ferric 
precipitate  by  omitting  the  bromine  and  using  considerable 
hydrochloric  acid  and  ammonia,  or  by  making  a  small  "basic 
acetate"  separation. 

The  filtrate  from  the  iron  contains  the  cobalt,  nickel,  and 
zinc.  These  may  be  determined  by  method  1,  Chapter  XIII. 
The  process,  just  described,  is  rather  slow  and  requires  much 
manipulation,  but  is  capable  of  giving  exact  results  for  all  im- 
purities in  copper  except  gold,  iron,  and  lead. 

ELECTROLYTIC    SEPARATIONS 

2.  Arsenic,   Antimony,   and    Tin    in    Crude    Copper.  —  The 

original  methods  1  have  been  modified  and  improved  by  Heber- 
lein,  Heath,  and  Brownson,2  in  order  to  adapt  them  to  rapid 
routine  work.  Electrolytic  separations,  however,  cannot  be  con- 
sidered as  reliable  as  methods  6,  7,  8,  in  which  the  arsenic 
group  is  separated  from  the  bulk  of  the  copper  by  a  special 
precipitant.  It  is  never  safe  to  assume  that  the  first  cathode 
from  casting,  or  converter,  metal  is  absolutely  pure.  The  first 
cathode  should  be  redissolved  in  nitric  acid,  or  diluted  "acid 
mixture/'  and  the  solution  electrolyzed  a  second  time,  until  the 
copper  is  entirely  removed. 

(a)  Arsenical  Lake  Copper.  —  With  metal  containing  .05  to 
.1  per  cent  of  arsenic,  10  grams  of  drillings  may  be  dissolved  in 
70  c.c.  of  " assay  solution"  and  the  solution  electrolyzed  for 
copper  as  described  in  method  2,  Chapter  XI.  When,  the  metal 
contains  only  .05  per  cent  arsenic,  two  electrolytes  may  be 
combined,  the  washings  added,  and  the  whole  solution  treated 
for  arsenic.  For  metal  containing  more  than  .05  per  cent 

1  Trans.  A.  I.  M.  E.  27,  962.  2  A.I.M.E.  Bull  80  (1913),  1489. 


DETERMINATION  OF  -FOREIGN  ELEMENTS  IN  COPPER     195 

arsenic,  methods  6  and  7  are  mor.e  accurate.  (It  is  easy  to  lose  a 
little  arsenic,  partly  by  volatilization,  partly  by  deposition  on 
the  copper  if  the  current  is  noff*  interrupted  at  the  right  time.) 
When  the  arsenic  is  well  oxidized  and  such  loss  is  avoided,  the 
electrolytic  method  may  show  .005  per  cent  higher  results  for 
arsenic  than  other  methods,  unless  one  can  eliminate,  before 
titration,  a  trace  of  platinum  which  may  be  carried  into  solution 
from  the  anode.  This  platinum  may  be  partially  removed  by 
fractional  precipitation  with  hydrogen  sulphide  water.  Combine 
the  electrolyte  and  washings,  remove  the  nitric  acid  by  a  second 
evaporation  to  dryness,  dilute  to  150  c.c.,  add  to  the  hot  liquid 
1  c.c.  of  strong  hydrogen  sulphide  water,  and  filter  after  five 
minutes.  Repeat  the  operation  as  long  as  a  brown  tint  is 
formed  at  once  without  any  yellow  precipitate. 

Then  proceed  to  the  separation  of  the  arsenic  according  to 
method  6b. 

(b)  Rapid  Method.  —  An  approximate  assay  of  refined  arseni- 
cal copper,  free  from  antimony,  may  be  quickly  obtained  by 
direct  reduction  and  titration  of  the  electrolyte  from  which  the 
copper  has  been  removed.  Transfer  the  electrolytes  to  a  500  c.c. 
beaker,  add  3  grams  of  potassium  bisulphate,  and  evaporate  on 
the  hot  plate  until  fumes  of  sulphur  trioxide  have  been  evolved 
for  five  minutes. 

Cool  the  liquid,  wash  it  into  a  long-necked  Kjehldahl  flask  of 
Jena  glass,  place  the  flask  in  an  inclined  position  over  a  small 
flame,  and  boil  off  the  water.  Allow  to  fume  for  five  minutes 
again,  and  when  the  time  is  nearly  up,  flash  the  neck  of  the  flask 
with  another  lamp  flame  long  enough  to  drive  out  any  trace  of 
nitric  or  sulphuric  acid  which  may  have  condensed.  This 
double  fuming  process  is  the  secret  of  success  with  the  method 
of  reduction  to  be  described.  After  the  flask  has  partly  cooled, 
add  from  a  paper  .5  gram  of  coarsely  powdered  tartaric  acid  and 
digest  until  the  solution  becomes  colorless,  giving  the  flask  an 
occasional  whirling  motion.  Allow  to  cool,  wash  into  a  400  c.c. 
beaker,  and  fill  the  beaker  about  half  full  of  water.  Drop  a 
small  piece  of  litmus  paper  into  the  beaker,  add  ammonia  until 
the  liquid  is  just  alkaline,  and  then  make  the  solution  acid  with 
sulphuric  acid,  adding  only  one  drop  in  excess.  Several  such 
digestions  may  be  conducted  at  once.  Place  the  beakers  in  a 
pan  of  water  to  cool,  then  carefully  neutralize  each  solution  with 


196  ANALYSIS  OF  COPPER 

8  to  10  grams  of  pure  sodium  bicarbonate.  Add  5  drops  of  a 
10  per  cent  solution  of  potassium  iodide,  3  c.c.  of  starch  solu- 
tion, and  titrate  with  iodine  as  in  method  6.  A  blank  test 
should  be  made  with  each  new  lot  of  reagents,  and  the  iodine 
reading  of  about  .2  c.c.  deducted  from  each  burette  reading 
obtained  in  the  analyses. 

3.  Rapid  Electrolytic  Method  for  Arsenic  and  Antimony 
in  Anodes.  —  The  direct  reduction  and  titration  of  an  electrolyte 
(method  2b)  is  only  intended  for  rough  work.  The  following 
separation  of  E.  E.  Brownson  is  more  accurate,  although  less 
reliable  than  the  distillation  and  reduction  methods  6,  7,  8. 
Treat  10  grams  of  the  sample  in  a  750  c.c.  beaker  with  30  c.c.  of 
sulphuric  acid,  20  c.c.  of  nitric  acid,  and  50  c.c.  of  water.  Drive 
off  red  fumes,  add  water  until  two-thirds  full,  and  electrolyze 
about  two  and  a  half  hours  at  4  amperes.  The  metal  may  be 
deposited  on  a  large  platinum  gauze  cylinder  having  the  following 
dimensions:  height,  7.5  cm.;  diameter,  7.5  cm.  The  gauze  is 
made  of  wire  .22  mm.  in  diameter  with  36  meshes  to  the  inch 
(or  14  per  cm.)  and  is  strengthened  by  rings.  The  deposition 
is  continued  until  the  solution  contains  about  .25  gram  of 
copper.  It  then  has  a  faint  blue  color.  The  cathode  is  rinsed 
with  a  jet  when  removed  from  the  solution.  The  acids  are 
now  neutralized  with  ammonia  and  the  solution  made  acid 
with  hydrochloric  acid,  adding  2  or  3  c.c.  in  excess.  Pass  a 
rapid  stream  of  hydrogen  sulphide  for  about  30  minutes  and 
allow  to  settle  for  about  30  minutes.  Filter  through  a  12.5  cm. 
paper  (C.  S.  &  S.)  in  a  7.5  cm.  funnel,  discarding  the  filtrate. 
Wash  once  on  the  paper  with  water  and  then  wash  the  sulphides 
into  a  No.  3  (or  tall  No.  5)  beaker  with  the  smallest  possible 
amount  of  water.  Place  the  beaker  containing  the  sulphides 
under  the  funnel  and  dissolve  any  sulphides  still  adhering  to  the 
filter  with  25  to  30  c.c.  of  hot  aqua-regia  poured  carefully  around 
the  edges  of  the  paper.  It  is  usually  well  to  pour  about  10  c.c. 
of  the  aqua-regia  into  the  original  beaker  and  transfer  from  it  to 
the  paper,  as  sometimes  a  film  of  antimony  forms  on  the  bottom 
of  the  first  beaker.  To  prevent  destruction  of  paper  the  acid 
may  be  diluted  one-fourth  with  water,  although  the  whole  must 
be  very  hot  to  attack  the  sulphides.  Wash  the  No.  5  beaker 
and  paper  with  a  small  amount  of  water  only,  as  extra  solution 
above  that  consistent  with  good  work  means  extra  time  for 


DETERMINATION  OF  'FOREIGN  ELEMENTS  IN  COPPER     197 

evaporation.  Cover  the  beaker,  .boil  about  30  minutes  to  break 
up  sulphides  and  remove  the  'cover,  washing  beaker,  and  cover 
with  a  fine  jet.  Continue  the  evaporation  to  complete  dryness, 
at  a  temperature  just  high  enough  not  to  cause  loss  by  spatter- 
ing, and  heat  until  the  residue  has  no  acid  odor. 

Add  about  4  or  5  grams  of  potassium  hydroxide,  30  c.c.  of 
water,  and  boil  vigorously  for  10  to  15  minutes.  All  arsenic 
and  antimony  will  go  into  solution.  Add  25  c.c.  of  strong 
sodium  sulphide  solution  (450  grams  of  fresh  monosulphide  crystals 
in  2  liters  of  water),  and  boil  vigorously  for  5  or  10  minutes. 
Allow  to  cool,  decant  the  clear  liquid  through  an  11  cm.  paper 
(C.  S.  &  S.  597)  into  a  250  c.c.  beaker,  again  add  25  c.c.  of  the 
strong  sodium  sulphide  solution  to  the  black  sulphide  in  the 
beaker,  stir  well  and  filter  off,  washing  well  with  a  jet  of  dilute 
sodium  sulphide  (450  grams  to  8  liters).  If  the  mass  is  kept 
very  wet  to  prevent  oxidation  of  copper  sulphide,  hot  water 
may  be  used  instead.  Add  5  c.c.  of  strong  hydrogen  peroxide 
to  the  diluted  filtrate  (volume  150  to  175  c.c.),  and  heat  until 
the  strong  yellow  color  fades.  Unless  too  much  organic  matter 
has  been  dissolved  from  the  paper,  the  liquid  should  become 
nearly  colorless. 

Antimony.  —  Cool  the  liquid  and  electrolyze  over  night  at 
from  .10  to  .15  ampere  per  square  decimeter  of  cathode  surface. 
Antimony  alone  is  precipitated.  In  the  morning,  remove  the 
cathode  with  a  very  rapid  motion  and  carefully  wash  the  adher- 
ing solution  into  a  clean  500  c.c.  beaker  with  a  jet  of  water. 
Wash  the  deposit  in  water  and  two  changes  of  alcohol,  dry  care- 
fully over  an  alcohol  flame,  and  weigh  the  antimony.  The  best 
cathode  is  an  ordinary  split  foil  which  has  been  roughened  by 
long  use. 

Arsenic.  —  Transfer  the  solution  entirely  to  the  500  c.c. 
beaker  and  make  distinctly  acid,  using  dilute  sulphuric  acid  (1 
part  to  4  of  water).  Pass  a  strong  current  of  hydrogen  sulphide 
for  about  ten  minutes,  allow  to  settle  for  twenty  to  twenty-five 
minutes,  and  filter  through  an  11  cm.  paper,  which  will  retain 
the  arsenic  but  not  the  finely  divided  sulphur.  It  is  best  to 
decant  the  clear  liquid,  only,  through  the  paper,  then  transfer 
the  heavy  sulphide  and  sulphur  with  remaining  solution  directly 
to  a  200  c.c.  beaker  by  a  jet  of  water.  Now  decant  any  excess 
of  water  from  the  No.  2  beaker  through  the  paper  and  place  this 


198  ANALYSIS  OF  COPPER 

No.  2  beaker  and  contents  under  the  funnel.  Dissolve  the 
small  amount  of  arsenic  on  the  paper  into  the  beaker  with 
dilute  ammonia  (1  to  4  of  water).  It  is  best  to  wash  down  the 
sides  of  the  500  c.c.  beaker  with  10  to  15  c.c.  of  this  dilute 
ammonia  in  order  to  recover  any  adhering  arsenic.  Then  pour 
this  washing  around  the  edges  of  the  filter,  wash  the  large  beaker 
with  the  jet,  and  allow  all  the  washings  to  run  into  the  small 
beaker. 

Make  the  contents  of  the  beaker  acid  with  sulphuric  acid 
and  add  7  or  8  c.c.  in  excess.  Evaporate  to  fumes  of  sulphur 
trioxide  at  a  temperature  just  high  enough  not  to  cause  loss  by 
spattering,  and  then  raise  to  a  very  high  heat  for  one  hour  to  an 
hour  and  a  half.  Cool,  wash  the  rim  and  the  sides  of  the  beaker 
very  thoroughly  with  water,  add  water  to  half  fill  the  beaker, 
neutralize  the  acid  with  ammonia,  make  slightly  but  distinctly 
acid  with  hydrochloric  acid,  and  filter  through  an  11  cm.  paper 
into  a  500  c.c.  beaker,  washing  well  with  hot  water.  Add  water 
to  half  fill  this  beaker,  neutralize  the  acid  with  sodium  bicar- 
bonate, and  add  3  or  4  grams  in  excess.  Cool  to  room  tempera- 
ture and  titrate  with  iodine.  Solution  21  of  Chapter  III  may 
be  employed.  The  author  quoted  prefers  to  dissolve  5.105 
grams  of  " reagent"  iodine  in  a  little  water  with  8.5  grams  of 
potassium  iodide  and  dilute  to  one  liter.  Then  1  c.c.  equals 
.0015  gram  arsenic.  The  next  method  is  another  variation  of 
the  electrolytic  separation. 

4.  Electrolytic  Separation  of  Foreign  Metals  from  Mansfeld 
Copper.1  —  Twenty  grams  of  sample  are  dissolved  in  a  beaker 
(10  X  17  cm.)  with  160  c.c.  of  nitric  acid  (d.,  1.2);  the  solution 
diluted  to  1  liter  and  electrolyzed  after  the  addition  of  20  c.c. 
of  sulphuric  acid  (d.,  1.2).  A  platinum  cylinder,  6  cm.  x  10  cm., 
is  used  as  a  cathode  with  a  spiral  anode;  current,  1  ampere  at 
2.3  volts  tension  across  the  terminals;  and  time,  twenty-four  to 
thirty  hours.  Dr.  Toisten  of  the  same  Company  uses  a  gauze 
cathode  with  an  anode  revolving  at  500  to  600  revolutions  per 
minute,  then  separates  the  arsenic  from  the  remaining  liquid  and 
distills  it  (according  to  E.  Fischer-Hufschmidt-Classen). 

H.  Koch  estimates  arsenic  in  a  special  sample,  but  determines 
the  antimony,  with  any  tin  present,  by  the  following  treatment 
of  the  electrolyte  from  which  the  copper  has   been   removed.— 
1  Hermann  Koch,  personal  communication. 


DETERMINATION  OF  FOREIGN  ELEMENTS  IN  COPPER     199 


Wash  off  the  cathodes  of  copper  -and  concentrate  the  liquid  to 
fumes  of  sulphur  trioxide.  Take  up  the  residue  in  water  with 
25  to  30  c.c.  of  hydrochloric  acTd  (d.,  1.2)  and  warm;  then 
transfer  the  clear  solution  to  a  beaker  and  treat  with  hydrogen 
sulphide  in  excess.  Filter,  and  wash  the  sulphides  with  hydrogen 
sulphide  water.  Evaporate  the  main  solution  to  fumes  with  the 
addition  of  a  little  nitric  acid,  and  determine  iron,  nickel,  and 
zinc  by  the  methods  described  in  Chapter  XIII. 

To  recover  antimony  (and  tin  if  present),  the  sulphides  are 
dissolved  in  the  original  beaker  at  a  gentle  heat  by  treatment 
with  30  c.c.  of  ammonium  sulphide.  The  paper  and  copper 
sulphide  are  washed  with  ammonium  sulphide  water,  and  the 
antimony,  in  solution,  deposited  in  a  250  c.c.  beaker  on  a  plati- 
num cylinder  of  66  sq.  cm.  total  surface.  With  a  current  of  .5 
ampere,  .05  gram  may  be  deposited  in  three  to  four  hours,  while 
arsenic  remains  in  solution. 

It  should  be  observed  that  antimony  deposits  alone  from 
solution  in  sodium  sulphide  (methods  3,  5);  while  antimony  and 
tin  precipitate  together  from  ammonium  sulphide.  Electrolytic 
separations  from  alkaline  sulphides  are  more  suited  to  con- 
siderable amounts  of  the  elements  deposited.  Compare  this 
with  the  electrolysis  (10)  in  acid  ammonium  oxalate  in  which 
an  accurate  deposition  of  pure  tin  is  obtained. 

5.  Electrolytic  Separation  of  Antimony  from  Tin.  —  In  the 
preceding  methods  a  little  trouble  is  sometimes  experienced  from 

ANTIMONY  FROM  TIN 


Rev. 
per  m. 

Weight 
Anti- 
mony 

Vol. 
cc. 

Reagents 
in.  Electrolyte 

Amp. 

Cathode 
Density 

Volt- 
age 

Temp. 
°C. 

Time 
Min. 

Maybe 
separated 
from- 

80  g.  NaoS  cryst. 

300- 

.05  to 

120. 

6.5g.  KCN. 

.5  to 

1.1  to 

60- 

40- 

0.5  to  .6 

400. 

•  10  g. 

2.     g.  KOH. 

1 

1.75 

.9 

50. 

50. 

g.  of  tin 

as  chlo- 

ride 

the  deposition  of  a  trace  of  sulphur  with  the  antimony.  The 
formula  for  the  electrolyte  in  this  alternative  method  was 
devised  by  Dr.  Toisten  as  an  improvement  on  the  original 
method  of  Classen.  Proceed  as  in  3  or  4,  using  hot  sodium 
sulphide  as  the  agent  of  extraction;  then  bring  the  solution  to 


200  ANALYSIS  OF  COPPER 

the  conditions  of  density,  temperature,  and  volume  noted  in  the 
table.  Wash  the  deposit  with  water  and  alcohol,  dry  at  105° 
C.,  and  weigh. 

SPECIAL  METHODS  FOR  ARSENIC,  ANTIMONY,  AND  TIN  IN 
REFINED    COPPER 

6.  By  Precipitation  with  Ferric  Hydroxide  and  Ammonia.  — 

In  its  present  form,  this  separation  has  been  developed  by  A.  M. 
Smoot  and  F.  D.  Greenwood,  with  modifications  by  W.  H. 
Bassett  and  Alden  Merrill.  In  the  combination  method  7  the 
author  makes  use  of  the  same  principle.  Ferric  hydroxide,  when 
precipitated  from  a  copper  solution  by  a  slight  excess  of  ammonia, 
forms  insoluble  compounds  with  any  arsenic  and  antimony 
present,  if  they  have  been  oxidized  to  the  pentavalent  condition 
during  the  solution  of  the  copper.  The  compounds  of  lower 
oxidation  are  relatively  more -soluble. 

Method.  —  Dissolve  25  to  50  grams  of  " casting"  copper  in  a 
liter  beaker  in  100  or  200  c.c.  of  nitric  acid  (d.,  1.42).  Boil  off 
the  red  fumes  and  evaporate  off  acid  for  fifteen  minutes  by 
letting  the  solutions  stand  without  cover-glasses  in  the  center 
of  the  hot  plate.  Dilute  to  300  c.c.  and  the  liquid  will  be  ready 
for  the  iron  treatment. 

To  analyze  " high-grade"  metal,  treat  100  grams  in  an  1800 
c.c.  beaker  with  400  c.c.  of  nitric  acid  (d.,  1.42).  Take  the 
solution  off  the  hot  plate  and  let  it  cool;  add  cold  water  to  make 
the  volume  500  c.c.  Neutralize  with  ammonium  hydroxide 
until  just  enough  copper  hydroxide  has  formed  to  sparsely  cover 
the  bottom  of  the  beaker;  then  add  about  5  grams  of  crystallized 
ferric  ammonium  sulphate  in  aqueous  solution  and  add  hot 
water  to  the  beaker  until  the  volume  is  about  1000  c.c.  for  a 
100-gram  sample  (or  500  c.c.  for  50  grams  of  copper).  For  a 
100-gram  sample  of  wire-bar  copper,  A.  M.  Smoot  recommends 
.5  gram  of  ferrous  sulphate  crystals,  but  results  will  be  more 
trustworthy  if  2  grams  are  used.  As  a  general  rule,  the  iron 
should  be  at  least  10  times  the  weight  of  the  arsenic  and  anti- 
mony, or  20  times  that  of  the  selenium  and  tellurium,  if  the 
latter  are  to  be  precipitated  with  the  arsenic,  as  in  7. 

Boil  the  solution  for  one  half-hour,  remove  from  the  plate, 
and  add  cold  water  until  the  volume  is  about  1500  c.c.  for  a 
100-gram  sample.  Allow  to  settle  for  a  period  of  one  to  five 


DETERMINATION  OF  FOREIGN  ELEMENTS  IN  COPPER    201 

hours;  that  is,  until  a  trial  proves  that  the  liquid  will  yield  a 
clear  filtrate.  Filter  on  a  15  cm.  paper  supported  by  a  platinum 
cone,  wash  the  precipitate  several  times  with  hot  water  until 
nearly  all  the  soluble  copper  is  washed  out.  It  is  possible  to 
neutralize  the  solution  with  ammonia  just  far  enough  to  provide 
a  slight  excess,  only,  beyond  the  amount  necessary  to  react  with 
the  ferric  sulphate  on  boiling.  A  very  little  basic  copper  should 
remain  in  the  washed  precipitate,  or  a  little  iron  may  be  held 
in  solution  with  resultant  loss  of  a  trace  of  antimony.  In  the 
analysis  of  any  material  containing  more  than  .002  per  cent  of 
arsenic,  the  author  adds  one  gram  of  the  ferric  salt  to  the  clear 
filtrate.  A  few  drops  of  ammonia  should  then  be  added  until  a 
slight  precipitate  appears,  the  solution  heated  to  boiling,  settled 
for  a  short  time,  and  again  filtered,  but  on  a  separate  paper. 
All  nitrates  must  be  removed  from  the  ferric  hydroxide,  generally 
by  re-precipitation. 

If  bismuth  is  present,  a  drop  of  hydrochloric  acid  and  a 
little  ammonium  carbonate  may  be  added  during  the  precipita- 
tion, using  such  an  excess  of  ammonia  that  .2  to  .3  gram  of 
copper  will  be  rendered  basic.  This  copper  salt  is  afterwards 
removed  by  dissolving  the  precipitate  in  a  little  dilute  nitric 
acid,  and  re-precipitating  with  a  considerable  excess  of  ammonia 
to  dissolve  the  basic  salt  of  copper.  Although  arsenic  may  be 
separated  from  antimony  and  tin  by  gravimetric  methods  (9, 10), 
the  distillation  of  the  arsenic  as  arsenious  chloride  is  the  most 
rapid  separation,  and  may  be  made  very  accurate  by  the  obser- 
vance of  certain  conditions.  As  contributors  have  given  no 
adequate  explanation  of  the  conditions  necessary  for  the  com- 
plete reduction  and  evolution  of  the  arsenious  chloride,  a  personal 
study  has  been  made.  The  most  important  ingredient,  besides 
hydrochloric  acid,  which  should  be  present  in  the  distilling  flask, 
is  a  salt  of  copper,  in  amount  equivalent  to  about  .5  gram  of 
the  crystallized  cuprous  chloride.  In  the  absence  of  this  metal, 
the  evolution  of  arsenic  is  apt  to  be  very  incomplete.  In  the 
distillation  of  arsenic  from  solutions  of  ores  and  mattes,  the 
saturated  double  chloride  of  copper  and  zinc  is  employed.  See 
method  6,  Chapter  VI. 

Since  acids  may  contain  traces  of  arsenic,  the  proper  acid  to 
use  in  distillation  is  the  pure  hydrochloric  acid  now  made  by 
the  electrolytic  process.  A  careful  blank  analysis  and  distillation 


202  ANALYSIS. OF  COPPER 

should  be  carried  through,  and  the  still  should  not  be  allowed 
to  cool,  until  the  last  addition  of  acid  and  distillation  has  been 
completed.  If  the  flask  cools  and  the  stopper  is  washed  .down  by 
fresh  acid,  a  little  more  iodine  would  be  required,  in  subsequent 
titration  of  the  distillate,  due  to  increased  action  on  the  rubber 
stoppers. 

Three  successive  distillations  are  generally  necessary  to 
remove  every  trace  of  arsenic  from  the  flask,  and  in  the  last 
two,  a  reducing  agent  is  introduced,  which  reduces  both  iron 
and  arsenic  to  the  lower  chlorides.  Ferrous  chloride  or  sulphate 
was  formerly  employed;  the  latest  and  most  effective  substance 
is  hypophosphorous  acid,  which  should  not  be  added  in  too  great 
excess  at  first  or  arsenic  may  be  reduced  to  the  black  metallic 
condition.  In  presence  of  selenium,  tellurium,  or  much  anti- 
mony, the  distillation  should  be  made  with  chlorides  free  from 

sulphuric  acid. 

ARSENIC 

6a.  Distillation  of  Arsenic  with  Hypophosphorous  Acid  as 
Reducing  Agent.  —  The  ferric  hydroxide  precipitate,  produced 
in  the  treatment  of  the  copper  solution,  is  dissolved  in  warm 
hydrochloric  acid  (15  to  25  parts  to  75  of  water).  Transfer  the 
solution  with  the  aid  of  a  little  strong  hydrochloric  acid  to  a 
300  c.c.  Erlenmeyer  flask,  through  a  60  c.c.  glass-stoppered 
separatory  funnel.  The  delivery  tube  is  bent  into  inverted  U 
form,  and  filed  at  a  sharp  angle  on  each  end  to  prevent  any 
chloride  of  iron  from  being  carried  over  mechanically.  The  flask 
is  connected  by  the  delivery  tube  and  black  rubber  stoppers  to 
the  top  of  a  vertical  8-inch  (20  cm.)  Allihn  condenser,  the  lower 
end  of  which  is  just  sealed  by  150  c.c.  of  water  contained  in  a 
400  c.c.  beaker.  A  few  glass  beads  in  the  flask  will  prevent 
bumping  during  distillation.  (See  Fig.  15.) 

The  covered  beaker  may  be  supported  on  an  adjustable  ring. 
By  lowering  this  gradually  as  the  distillations  progress,  the  seal  is 
preserved,  but  the  solution  can  never  rise  any  higher  than  the 
first  bulb  of  the  condenser  without  breaking  the  seal.  Reverse 
suction  is  thus  avoided.  With  this  precaution,  a  dozen  stills 
may  be  run  by  one  operator.  The  total  amount  of  hydrochloric 
acid  in  the  still  should  be  50  c.c.  As  the  ferric  hydroxide 
was  reprecipitated  and  the  copper  removed  in  the  ammonia 
treatment,  .5  gram  of  cuprous  chloride  should  be  added  to 


DETERMINATION  OF  FOREIGN  ELEMENTS  IN  COPPER    203 


the  flask  before  the  solution  is,  introduced.  Distill  until  the 
volume  is  reduced  to  about  20*  c.c.  (One  operator  distills  for  a 
half-hour  longer,  adding  concentrated  hydrochloric  acid  to 
replace  that  which  distills  over.)  To  be  sure  of  the  complete 
evolution  of  arsenic  from  any  sample,  add  30  c.c.  of  strong 
hydrochloric  acid  to  the  residue  from  the  first  distillation  without 
cooling  the  flask,  and  follow  with  .5  c.c.  of  50  per  cent  hypo- 
phosphorous  acid.  Distill  down 
again  to  about  20  c.c.  Without 
cooling,  add  30  c.c.  more  strong 
hydrochloric  acid  with  .5  c.c.  of 
the  50%  hypophosphorous  acid 
and  distill  a  third  time.  If  any 
doubt  exists  as  to  the  complete- 
ness of  the  evolution,  another 
distillation  with  more  acid  may 
be  continued  for  fifteen  minutes, 
and  the  distillate  collected  in 
a  separate  beaker,  and  treated 
by  itself. 

6b.  —  Distillation  with  Fer- 
rous Salt  as  Reducing  Agent.  — 
In  this  older  method,  the  ferric 
hydroxide  is  dissolved  in  3  to  10 
c.c.  of  sulphuric  acid  diluted 
with  5  parts  of  water  and  trans- 
ferred to  the  Erlenmeyer,  or 
round-bottomed  Jena  flask. 
Smoot  prefers  to  add  enough  acid 
to  make  the  total  amount  5  to  6 
c.c.  for  high-grade  copper  samples, 
then  evaporate  to  fumes  by 
shaking  the  flask  over  a  naked 
Bunsen  flame  and  directing  a 
gentle  current  of  air  into  the  flask.  The  flask  is  then  cooled, 
and  2  c.c.  of  water  and  2  grams  of  ferrous  sulphate  are  added. 
Connect  with  the  Allihn  condenser,  add  60  c.c.  of  strong  hydro- 
chloric acid  and  distill  down  to  about  25  c.c.,  then  add  40  c.c. 
more  of  strong  hydrochloric  acid  and  distill  again  to  a  volume 
of  25  c.c.  Some  operators  now  prefer  to  remove  the  distillate, 


Fig.  15.  —  Distillation  Apparatus. 


204  ANALYSIS  OF  COPPER 

add  40  c.c.  more  acid,  repeat,  and  test  the  last  distillate  by 
itself.  With  miscellaneous  samples,  there  is  no  advantage  in 
separating  the  distillates.  If  the  last  distillate  does  not  show 
any  more  test  by  titration  with  iodine  than  would  be  obtained 
by  distilling  40  c.c.  of  acid  with  pure  copper  salt  and  reducer, 
the  operation  is  finished.  When  the  distillate  is  titrated  with 
iodine,  a  slight  blank  will  be  obtained  from  the  purest  hydro- 
chloric acid,  due  to  its  action  on  the  rubber  stoppers.  As 
already  stated,  this  distillation  from  a  solution,  which  at  the 
end  contains  very  strong  boiling  sulphuric  acid,  is  rather  uncer- 
tain in  presence  of  selenium  and  tellurium,  which  are  somewhat 
volatile  under  the  conditions  specified.  Chloride  of  antimony 
begins  to  volatilize  at  120-122°  C.,  and  the  temperature  of  the 
liquid  in  the  flask  should  not  rise  above  118°. 

With  the  hydrochloric  acid  and  chlorides  (a),  arsenic  has  been 
separated  by  distillation  from  .01  gram  of  selenium  and  tellurium. 

If  sulphuric  acid  is  distilled  too  far,  in  presence  of  the  first 
reducer  described  (a),  it  may  be  slightly  decomposed,  thus  in- 
juring the  distillate. 

6c.  Treatment  of  the  Distillate  by  Hydrogen  Sulphide. — 
To  finish  the  analysis  by  the  slower  gravimetric  modification, 
proceed  to  charge  the  cold  or  slightly  warm  solution  with 
hydrogen  sulphide,  until  it  smells  strongly  of  the  gas.  Allow 
to  settle  and  filter  the  yellow  arsenious  sulphide  on  a  weighed 
Gooch  crucible  which  has  been  made  up  with  a  paper  disc  and 
acid-washed  asbestos,  and  dried  at  100°  C.  before  weighing. 
Extract  the  yellow  salt  with  alcohol  followed  by  carbon  bisul-' 
phide.  Wash  finally  with  alcohol  and  ether  and  dry  in  an  oven 
at  100°  C.,  or  less.  The  principal  objection  to  this  modification 
is  the  difficulty  experienced  in  extracting  every  trace  of  sulphur 
by  volatile  solvents. 

6d.  Titration  of  Arsenious  Acid  by  Iodine.  —  Distillates, 
containing  no  more  than  traces  of  arsenious  compounds,  may  be 
titrated  with  a  definite  and  sharp  end-point,  if  a  little  am- 
monium sulphate  is  present  at  the  time  of  titration,  and  if  4  or 
5  drops  of  a  10  per  cent  solution  of  potassium  iodide  are  added 
to  the  distillate  after  it  has  been  completely  neutralized  with  a 
large  excess  of  sodium  bicarbonate. 

To  prepare  a  solution  for  titration,  dilute  the  clear  liquid 
resulting  from  the  digestion  prescribed  in  the  next  method  (7), 


DETERMINATION  OF  FOREIGN  ELEMENTS  IN  COPPER    205 

or  the  hydrochloric  acid  distillate  from  the  preceding  (6),  until 
the  volume  is  about  200  c.c.  Neutralize  with  strong  ammonia, 
using  a  floating  piece  of  litmus  paper  as  an  indicator.  If  the 
solution  becomes  very  warm,  cool  it  during  neutralization  by 
standing  the  beaker  in  a  large  pan  of  cold  water.  Bring  the 
liquid  back  to  a  slightly  acid  reaction  by  a  few  drops  of  dilute  sul- 
phuric acid.  To  the  cold,  faintly  acid  solution,  add  gradually  8  to 
10  grams  of  pure  sodium  bicarbonate,  keeping  the  beaker  covered. 
Wash  off  the  cover,  add  4  to  5  drops  of  the  potassium  iodide, 
3  c.c.  of  starch  indicator  (57,  Chapter  III),  and  titrate  with 
the  standard  iodine,  one  cubic  centimeter  of  which  oxidizes 
about  .001  gram  of  arsenic  (As).  Refer  to  solution  21,  Chapter 
III. 

To  standardize  the  iodine,  dissolve  weighed  portions  of  .06 
gram  of  chemically  'pure  arsenious  oxide  in  a  little  water  with 
the  aid  of  .5  to  1  gram  of  potassium  hydroxide.  Transfer  the 
solution  to  a  400  c.c.  beaker,  dilute  to  300  c.c.,  make  slightly 
acid  with  sulphuric  acid,  then  alkaline,  then  faintly  acid.  Treat 
with  the  excess  of  sodium  bicarbonate,  followed  by  the  trace  of 
potassium  iodide  and  starch,  and  titrate  with  the  iodine.  Correct 
for  the  slight  excess  of  about  .04  c.c.,  required  to  produce  the 
change  -of  color  from  red  to  a  purplish  blue.  The  temperature 
of  the  iodine  should  be  noted  at  the  time  of  standardization,  and 
correction  made  to  analyses  of  high-grade  copper,  for  any  appre- 
ciable variation  of  temperature.  As  the  iodine  solution  is  a 
little  viscous,  a  specified  time  should  be  allowed  for  the  draining 
of  the  burette,  —  say,  five  minutes  for  50  c.c.  of  reagent. 

Careful  blank  analyses  should  be  made  with  the  reagents 
under  the  same  conditions. 

7.  Combination  Method  (including  Selenium  and  Tellurium).1 
—  The  separation  is  nearly  the  same  as  that  of  the  preceding 
method,  but  an  excess  of  ammonia  is  employed  great  enough  to 
precipitate  all  the  copper  as  hydroxide  and  to  redissolve  it  to  a 
clear  solution  of  the  complex  salt.  Other  reagents  are  added  to 
complete  the  separation  of  antimony,  bismuth,  selenium,  and 
tellurium. 

If  the  metal  contains  less  than  .05  per  cent  of  arsenic,  50  to  100 
grams  of  copper  are  taken  for  each  analysis.  This  quantity  is  re- 
duced to  25  grams  with  arsenical  copper.  For  50  grams  of  copper 

1  By  author. 


206  ANALYSIS  OF  COPPER 

add  gradually  210  c.c.  of  nitric  acid  (d.,  1.42),  dilute  the  solution 
with  water  until  the  1500  c.c.  beaker  is  half  full,  and  introduce  5 
grams  of  ferric  ammonium  sulphate,  or  an  equivalent  amount  of 
ferric  sulphate.  Heat  nearly  to  boiling,  add  strong  ammonia 
until  the  basic  hydroxide  of  copper  has  formed  and  redissolved. 
This  requires  about  300  c.c.  If  bismuth  and  antimony  are  to 
be  determined,  add  (after  the  ammonia)  2  grams  of  ammonium 
carbonate  and  5  c.c.  of  saturated  solution  of  sodium  phosphate. 
Bring  to  a  boil,  allow  to  settle  for  an  hour  on  the  steam  plate, 
and  filter  quickly  through  a  15  cm.  washed  filter,  supported  by 
a  platinum  cone  with  coarse  perforations.  Keep  the  solutions 
warm  to  prevent  crystallization,  and  wash  the  blue  color  out  of 
the  filter  with  dilute  (1  to  20)  ammonium  hydroxide.  Pass  the 
filtrate  through  a  second  filter  to  recover  traces  of  iron  which 
may  pass  the  first  paper. 

If  the  copper  contains  more  than  .005  per  cent  of  arsenic,  the 
filtrate  should  be  treated  a  second  time  with  iron  and  ammonia, 
using,  however,  just  enough  iron  salt  to  clean  the  solution. 
Make  the  first  filtrate  and  washings  acid  with  nitric  acid,  add  .5 
gram  of  oxidized  ferrous  sulphate,  or  1  gram  of  the  alum,  and 
sufficient  ammonia  to  complete  the  precipitation  as  before. 
Allow  to  settle  and  filter.  Preserve  this  hydroxide  separately. 
Wash  the  large  precipitate  of  ferric  hydroxide  into  a  400  c.c. 
beaker  and  dissolve  that  which  remains  on  the  paper  with  a 
little  hot  dilute  sulphuric  acid.  Wash  the  filter  with  a  little 
ammonia,  then  precipitate  the  ferric  hydroxide  with  ammonia, 
ammonium  carbonate  and  phosphate,  filtering  on  the  original 
paper.  Wash  out  the  copper  salts.  Clean  this  last  filtrate 
from  any  trace  of  arsenic,  etc.,  by  adding  to  it  the  solution  of 
the  small  precipitate  of  ferric  hydroxide,  which  was  reserved. 

Make  acid,  then  precipitate  again  with  ammonia,  filter,  and 
wash.  The  ferric  hydroxide  may  now  be  redissolved  in  40% 
hydrochloric  acid  and  the  arsenic  distilled  as  in  6a.  In  presence 
of  much  selenium  or  tellurium  proceed  as  follows: — 

Separation  of  Selenium  and  Tellurium.  — Transfer  all  the  iron 
precipitates  to  a  500  c.c.  beaker,  and  dissolve  any  precipitate 
adhering  to  the  papers  by  repeated  treatment  with  a  little  hot 
dilute  sulphuric  acid.  Record  the  amount  of  all  acids  used  in 
order  to  make  a  blank  test  of  the  reagents. 

To  remove  the  last  traces  of  bismuth,  or  antimony,  from  the 


DETERMINATION  OF  FOREIGN  ELEMENTS  IN  COPPER    207 

filters,  boil  the  papers  with  a  little  25  per  cent  hydrochloric  acid. 
Nitric  acid  of  15  per  cent  strength  will  extract  bismuth.  Pre- 
serve this  extract  as  "solution  B&  until  the  selenium  and  tellu- 
rium have  been  separated  from  the  sulphuric  acid  solution  of 
the  ferric  hydroxide.  The  following  separation  is  successful  as 
outlined,  only  when  hydrochloric  acid  is  not  present.  For  chlo- 
ride solutions,  use  Keller's  method  17  (Chapter  XIII). 

Heat  the  sulphate  solution  to  boiling  and  saturate  it  with  a 
rapid  current  of  sulphur  dioxide,  generated  as  described  in  Chap- 
ter III.  Continue  charging  for  one  hour  at  80  to  85°  C.,  or  until 
the  precipitate  has  formed,  and  allow  to  partially  cool  while  pass- 
ing the  gas.  Settle  over-night  on  the  work-table,  and  filter  the 
liquid  through  an  asbestos  felt  in  a  Gooch  crucible.  If  the  se- 
lenium is  to  be  separated  from  the  tellurium,  the  first  felt  need 
not  be  weighed.  For  weighing,  prepare  a  felt  with  acid-washed 
and  ignited  asbestos,  and  take  the  weight  of  ignited  felt.  Then 
moisten  the  felt  with  a  little  water,  dry  in  an  oven  for  one  hour 
at  105°  C.,  and  weigh  to  obtain  the  "dried  weight."  Dry  the 
washed  precipitate  of  selenium  and  tellurium  in  the  same  way,  and 
deduct  from  the  final  weight  the  "dried  weight"  of  the  pad.  As 
a  check,  the  weighed  felt  may  finally  be  ignited  at  a  red  heat, 
cooled  and  reweighed,  using  as  a  tare  the  original  "ignited  weight" 
of  the  pad.  Repeat  the  treatment  of  the  solution  with  sulphur 
dioxide  as  before  and  weigh  any  additional  selenium  and  tellurium. 
No  more  than  a  trace  should  appear.  For  the  separation  of  the 
two  elements,  refer  to  the  special  method  17,  Chapter  XIII. 

Arsenic  and  Antimony. — The  small  "solution  B"  should 
now  be  added  to  the  principal  solution  of  ferric  salt  and  the 
sulphur  dioxide  expelled  by  boiling.  Pass  a  rapid  current  of 
hydrogen  sulphide  through  the  warm  solution  for  fifteen  min- 
utes and  allow  to  stand  until  the  sulphides  appear  granular. 
Then  charge  again  with  the  same  gas  and  allow  to  settle  over- 
night. In  the  morning,  treat  with  hydrogen  sulphide  again  until 
the  liquid  smells  strong,  filter,  and  remove  the  sulphide  from 
the  beaker  with  the  aid  of  bits  of  paper  and  stiff  platinum  wire. 
Transfer  the  paper  and  contents  to  a  75  c.c.  beaker.  Heat  the 
main  solution  to  85°  C.  and  saturate  with  hydrogen  sulphide, 
settle,  filter,  and  repeat  this  treatment  as  long  as  a  trace  of 
yellow  sulphide  remains  on  the  filter  after  extraction  with 
alcohol  and  carbon  bisulphide. 


208  ANALYSIS  OF  COPPER 

Separation  of  Arsenic  from  the  Antimony  and  Tin.  —  The 
sulphides  may  be  transferred  directly  to  the  distilling  flask 
described  in  the  previous  method,  and  the  arsenic  directly  dis- 
tilled off  with  a  special  distilling  solution  according  to  method  1, 
Chapter  VI.  Precipitate  the  arsenic  as  in  6c,  or  titrate. 

The  arsenic  may  be  separated  gravimetrically  as  follows, — 
when  antimony  and  bismuth  are  to  be  determined  :  Digest  the 
sulphides  in  the  100  c.c.  beaker  on  the  hot  plate  with  20  to  30  c.c. 
of  a  mixture  of  sodium  monosulphide  (d.,  1.08)  and  2  parts 
of  water.  An  equal  part  of  potassium  sulphide,  or  hydroxide, 
should  be  added  to  the  sodium  sulphide  when  bismuth  is  present 
to  prevent  the  solution  of  a  trace  of  that  metal.  (A  satisfactory 
extraction  for  a  first  treatment  may  be  obtained  by  using  30  c.c. 
of  a  strong  solution  of  yellow  ammonium  sulphide,  containing 
1  gram  of  ammonium  chloride.  A  little  copper  sulphide  may, 
however,  be  dissolved,  in  which  case  a  slight  excess  of  potassium 
hydroxide  may  be  added  before  final  evaporation.)  Filter  the 
liquid  through  a  small  paper  and  wash  with  the  solvent,  diluted 
with  ten  parts  of  water.  The  sulphides  of  bismuth,  lead,  and 
copper  remain  insoluble.  The  clear  yellow  solution  is  taken  to 
dryness  on  a  steam  plate,  filtering  out  any  trace  of  black  sul- 
phide which  may  appear.  Treat  the  residue  with  20  c.c.  of  red, 
fuming  nitric  acid  (d.,  1.60  to  1.70),  and  digest  until  the  sulphur 
disappears.  Remove  the  cover  and  evaporate  to  dryness. 

The  next  step  is  to  separate  pure  sulphide  of  arsenic  from  a 
concentrated  hydrochloric  acid  solution.1  Dissolve  the  residue 
in  25  c.c.  of  water,  adding  a  small  crystal  of  tartaric  acid,  and, 
finally,  50  c.c.  of  hydrochloric  acid  (d.,  1.2).  Saturate  the  cold, 
or  slightly  warm,  solution  with  hydrogen  sulphide,  allow  to 
settle  for  ten  to  fifteen  minutes  only,  and  filter  on  an  asbestos 
felt,  or  paper  filter.  Wash  the  sulphide  with  acid  of  the  same 
strength,  and  remove  adhering  sulphide  from  the  beaker  with 
wads  of  asbestos,  or  paper.  Remove  the  flask,  or  bottle,  with 
the  filtrate,  then  wash  out  the  last  traces  of  acid  from  the  filter 
with  water  and  reject  the  washings.  Test  the  filtrate  again  with 
hydrogen  sulphide,  filter,  and  repeat  the  treatment  if  necessary. 
One  precipitation  should  be  sufficient,  however. 

Preparation  of  Arsenious  Compound  for  Titration.  —  The 
sulphide  may  be  dissolved  with  a  very  little  dilute  sodium  (or 
1  G.  A.  Heberlein,  Trans.  A.  I.  M.  E.  27,  967. 


DETERMINATION  OF  FOREIGN  ELEMENTS  IN  COPPER    209 

ammonium)  sulphide, — free  from  chlorides, — the  solution 
washed  into  a  300  c.c.  Kjehldanl  flask  of  Jena  glass;  the  liquid 
then  treated  with  25  c.c. , of  strong  sulphuric  acid  and  3  grams  of 
potassium  bisulphate,  and  evaporated  to  fumes.  It  is  necessary 
to  boil  hard  enough  to  expel  every  particle  of  sulphur  from  the 
neck  of  the  flask.  Add  .5  gram  of  crystals  of  tartaric  acid, 
rotate  the  flask,  digest  until  colorless,  cool,  dilute,  and  titrate 
as  directed  in  method  2b.  The  operation  of  digestion  in  the 
flask  is  more  rapid,  if  the  sulphur  is  all  destroyed  by  a  pre- 
liminary treatment  in  a  covered  beaker  with  fuming  nitric  acid. 
Evaporate  the  clear  solution  to  dryness  with  6  drops  of  sulphuric 
acid,  treat  with  25  c.c.  of  sulphuric  acid,  evaporate  again,  and 
fume  for  five  minutes.  Transfer  the  cooled  solution  to  the 
digestion  flask  and  proceed  as  in  2b,  observing  the  precautions 
for  the  removal  of  all  traces  of  nitric  acid. 

Any  bismuth  in  the  black  sulphides,  insoluble  in  alkalies, 
may  be  determined  by  methods  1  or  2,  Chapter  XIII. 

8.  Precipitation  of  Arsenic  Acid  by  Magnesia  Mixture.  — 
The  original  procedure  of  Fresenius  has  been  modified  to  secure 
a  more  complete  precipitation.  This  is  accomplished  by  redu- 
cing the  final  volume  of  the  solution  and  washings  to  the  lowest 
possible  limit.  This  accurate  method  is  only  used  at  present  as 
a  check,  the  more  rapid  process  of  distillation  and  titration  hav- 
ing the  preference  in  technical  work. 

Proceed  with  the  solution  of  copper  according  to  the  sixth  or 
seventh  method  until  the  pure  arsenious  sulphide  has  been 
separated.  If  the  copper  contains,  however,  but  a  trace  of 
antimony  and  the  reagents  or  distilled  water  show  no  trace  of 
tin,  it  is  not  necessary  to  make  any  preliminary  separation 
of  the  arsenic  from  antimony.  Evaporate  the  ammonium  sul- 
phide solution  of  the  arsenic  and  antimony  sulphides  to  dryness 
on  the  steam  plate,  adding  .1  to  .3  gram  of  sodium  nitrate. 
Treat  the  residue  (or  the  pure  sulphide  obtained  in  method  7)- 
with  20  c.c.  of  red-fuming  nitric  acid  and  digest  until  the  sulphur 
disappears.  Dilute  the  acid  with  one  and  one-half  parts  of 
water,  filter  out  any  insoluble  matter  on  a  small  paper,  wash,  add  5 
drops  of  sulphuric,  and  evaporate  the  solution  to  dryness  on  the 
steam  bath.  Now  'dissolve  the  salts  in  5  c.c.  of  cold  water  with  the 
addition  of  10  drops  of  hydrochloric  acid  and  .1  gram  of  tartaric 
acid.  Unless  the  arsenic  is  known  to  exceed  .05  gram,  filter 


210  ANALYSIS  OF  COPPER 

through  a  2.5  cm.  paper  into  a  25  c.c.  beaker.  Wash  with  a  few 
drops  of  water  from  a  fine  jet  and  make  slightly  alkaline  with 
strong  ammonia  (d.,  .90).  The  liquid  should  remain  clear;  if 
not,  make  the  solution  faintly  acid  and  add  another  portion  of 
tartaric  acid. 

Precipitation.  —  To  the  alkaline  solution  (volume  10  to  11 
c.c.)  add  3  c.c.  of  magnesia  mixture  (solution  23,  Chapter  III), 
dilute  to  20  c.c.  with  the  strong  ammonia,  and  stir  rapidly  for 
five  minutes.  If  the  arsenic  is  excessive,  use  a  50  c.c.  beaker 
for  precipitation,  increase  the  amount  of  magnesia  mixture  to 
5  to  10  c.c.,  and  add  ammonia  water  equal  to  one-third  of  the 
volume  of  the  solution. 

Allow  to  stand  overnight  in  a  cool  place,  filter  on  a  2.5  cm. 
or  3  cm.  washed  filter,  transferring  the  precipitate  to  the  paper 
by  pouring  a  little  of  the  filtrate  back  into  the  first  beaker. 
Wash  with  a  fine  jet  of  dilute  (1:3)  ammonia  until  the  washings 
test  nearly  free  from  chloride  when  acidified  and  treated  with  a 
drop  of  silver  nitrate.  Dry  the  filter  and  contents  in  an  oven 
at  100°  to  105°  C.,  remove  the  salt  as  completely  as  possible  to 
a  glazed  paper,  and  place  the  filter  in  a  weighed  porcelain  cru- 
cible. Add  a  few  drops  of  a  saturated  solution  of  acid  ammo- 
nium nitrate,  char  the  paper  very  carefully,  and  repeat  the 
treatment  at  low  heat  until  the  paper  is  consumed  without  a 
perceptible  odor  of  arsenic.  Transfer  the  remainder  of  the  salt 
with  the  aid  of  a  camel's-hair  pencil  and  ignite  very  slowly  until 
the  ammonia  is  driven  off,  then  at  a  full  red  heat  over  the  Bun- 
sen  burner  until  two  successive  weights  closely  agree. 

9.  Determination  of  the  Antimony,  — in  Absence  of  Tin. — The 
acid  liquid  remaining  in  the  flask  after  distillation  of  arsenic,  or 
the  filtrate  from  the  gravimetric  separation  of  arsenious  sulphide, 
contains  all  the  antimony  (and  tin).  The  liquid  remaining  in 
the  flask  from  a  distillation  process  may  also  contain  selenium, 
tellurium,  bismuth,  and  a  little  copper.  In  such  a  case,  dilute 
the  hydrochloric  acid  solution  until  it  contains  one  part  of  strong 
hydrochloric  acid  (d.,  1.2)  to  five  of  water,  and  pass  hydrogen 
sulphide  to  precipitate  the  metals.  Extract  the  soluble  sulphides 
as  in  methods  6,  7,  for  arsenic,  using  15  c.c.  of  a  colorless  15  per 
cent  solution  of  sodium  sulphide.  If  bismuth  is  present  add  a 
little  potassium  hydroxide,  or  treat  the  washed  sulphide  with 
hot,  dilute  potassium  hydroxide  alone  (Smoot).  Warm  the  sola- 


DETERMINATION  OF  FOREIGN  ELEMENTS  IN  COPPER    211 

tion  and  allow  to  stand  for  an  hour  or  more,  dilute,  filter  off  the 

$ 

sulphide  of  copper,  and  wash  the  paper  with  dilute  sodium  sulphide. 

Acidify  the  filtrate  with  dilute"  hydrochloric  or  sulphuric  acid, 
and  pass  hydrogen  sulphide  into  the  liquid  long  enough  to  en- 
sure an  excess.  Unless  absolutely  sure  of  its  purity,  it  is  well 
to  extract  this  antimony  sulphide  again  with  colorless  sodium 
sulphide  to  make  sure  that  no  copper  remains.  Then  acidify 
the  filtrate  with  dilute  acid  and  saturate  with  hydrogen  sulphide 
as  before.  The  antimony  sulphide  contains  more  or  less  sul- 
phur. It  is  best  to  filter  it  on  a  small  paper,  transfer  the  paper 
and  contents  to  a  small  beaker,  and  add  enough  fuming  nitric 
acid  to  make  the  solution  colorless  when  the  paper  is  destroyed. 
Bassett  and  Merrill  recommend  the  following :  Add  2  c.c.  of 
(1:1)  sulphuric  acid  and  evaporate  just  to  fumes  of  sulphur 
trioxide;  dilute,  add  1  or  2  c.c.  of  hydrochloric  acid,  filter  to 
remove  possible  silica,  etc.,  and  saturate  again  with  hydrogen 
sulphide.  This  precipitates  clean  antimony  sulphide.  Filter  on 
a  weighed  Gooch  crucible  made  up  with  a  paper  disc  and  as- 
bestos, extract  with  carbon  bisulphide,  wash  with  alcohol  and 
ether,  and  dry  in  an  oven  at  100°  C.  According  to  A.  M.  Smoot, 
the  last  two  precipitations  may  be  avoided  by  collecting  the 
antimony  sulphide  (if  free,  from  copper)  on  a  small  weighed 
asbestos  pad.  Wash  with  water  containing  hydrogen  sulphide 
and  suck  the  pad  quite  dry.  Add  a  single  drop  of  strong  nitric 
acid  which  should  not  saturate  the  pad.  Warm  the  crucible 
gently  until  the  acid  is  expelled  and  then  add  one  drop  of  fum- 
ing nitric  acid.  Do  this  very  carefully  to  avoid  saturation  and 
yet  reach  all  the  sulphide.  Warm  gently  to  expel  the  'acid, 
ignite  the  antimony  to  oxide  (Sb2O4),  and  weigh.  The  electro- 
lytic methods,  noted  at  the  beginning  of  this  chapter,  are  not 
suitable  for  copper  containing  only  a  trace  of  antimony. 

10.  Separation  of  Antimony  from  Tin.  —  Distilled  water  and 
acids  sometimes  contain  traces  of  tin.  If  the  antimonic  and 
stannic  acids,  resulting  from  the  oxidation  of  the  pure  sulphides, 
are  evaporated  to  dryness  with  five  drops  of  sulphuric  acid,  the 
residue  may  be  directly  treated  by  the  method  of  G.  W.  Thomp- 
son. The  antimony  is  precipitated,  alone,  by  hydrogen  sulphide 
from  a  special  solution,  and  the  filtrate  electrolyzed. 

Dissolve  5  grams  of  pure  oxalic  acid  and  5  grams  of  crys- 
tallized ammonium  oxalate  in  100  c.c.  of  water,  pour  the  mix- 


212  ANALYSIS  OF  COPPER 

ture  on  the  residue  to  be  tested,  and  boil  for  half  an  hour,  if 
necessary,  to  dissolve  the  salts.  If  sodium  sulphide  was  used 
in  the  first  extraction  of  the  soluble  sulphides,  a  little  silica  will 
remain  insoluble.  Filter  this  out,  and  wash  the  paper  twice. 
Treat  the  silica  in  a  platinum  dish  with  a  very  little  hydrofluoric 
acid  and  evaporate  to  dryness  with  a  little  hydrochloric  acid.  If 
any  residue  appears,  boil  it  with  a  little  acid-ammonium  oxalate 
mixture  and  add  it  to  the  principal  solution  of  the  antimony. 
Heat  the  oxalate  solution  to  boiling,  pass  hydrogen  sulphide  for 
fifteen  minutes,  filter  off  the  antimony  sulphide,  and  wash  with 
hydrogen  sulphide  water.  Saturate  the  hot  filtrate  again  with 
hydrogen  sulphide  and  filter.  If  considerable  tin  is  present,  a 
trace  may  be  held  in  the  paper.  To  remove  it,  dissolve  the 
sulphide  of  antimony  in  a  very  little  ammonium  sulphide,  pour 
the  solution  gradually  into  a  fresh  boiling  solution  of  the  mixture  of 
oxalic  acid  and  oxalate,  and  saturate  again  with  hydrogen  sulphide. 
One  separation  is  usually  sufficient  to  separate  a  trace  of  tin. 
The  presence  of  traces  of  tin  may  be  due  to  the  use  of  water, 
delivered  from  tin-lined  condensers. 

The  antimony  is  then  treated  as  directed  in  the  preceding 
method  9. 

Tin.  —  The  tin  may  now  be  recovered  from  the  acid  oxalate 
solution  by  direct  electrolysis.  This  gives  better  results  with 
small  amounts  of  tin  than  the  deposition  in  sulphide  solutions. 
Boil  out  the  hydrogen  sulphide,  cool  the  solution,  and  electro- 
lyze  with  a  current  of  .8  ampere  per  square  decimeter  of  immersed 
cathode  surface.  The  anode  should  be  rotated  500  times  per 
minute,  or  the  electrolyte  may  be  stirred  by  a  stream  of  air 
which  is  caused  to  bubble  up  under  an  inverted  funnel;  a  device 
recommended  by  J.  G.  Fairchild.  The  deposition  of  a  large 
amount  of  tin  may  be  completed  in  two  and  one-half  hours. 
The  end-point  is  indicated  by  a  cessation  of  the  gas  evolution 
and  by  a  slight  alkalinity  of  the  solution  to  litmus  paper.  Wash 
the  deposit  with  water,  alcohol,  and  ether.  Dry  gently  over  a 
lamp,  or  in  an  oven,  and  weigh.  Dissolve  the  deposit  in  dilute 
nitric  acid  and  correct  the  weight  of  the  tin  for  any  iron  which 
may  be  found  in  the  filtrate. 

Detection  of  Traces  of  Tin.  —  To  obtain  a  positive  indica- 
tion of  a  minute  amount  of  this  element,  the  older  gravimetric 
method  may  be  employed.  Evaporate  the  oxalate  solution  to 


DETERMINATION  OF  FOREIGN  ELEMENTS  IN  COPPER    213 

fumes  with  an  excess  of  sulphuric-acid,  following  the  removal  of 
the  antimony.  Dilute  the  acid  solution  and  precipitate  the  tin 
as  stannous  sulphide.  Filter,  wasfi,  ignite  slowly  in  a  weighed 
porcelain  crucible,  and  weigh  as  stannic  oxide.  Test  the  pre- 
cipitate for  copper  and  iron  by  fusion  with  a  pinch  of  sulphur 
and  sodium  carbonate  and  extraction  with  water. 

For  the  direct  determination  of  tin  in  copper,  without  regard 
to  other  elements,  consult  "  special  methods  for  tin,"  16,  Chapter 
XIII. 


CHAPTER  XIII 

SPECIAL  METHODS  FOR  FOREIGN   METALS  IN  COPPER 

BISMUTH 

1.  Determination  as  Oxy chloride.  —  One  description  will  be 
sufficient  for  the  similar  modifications  devised  by  A.  M.  Smoot 
and  H.  Koch.  The  principle  involved  is  the  precipitation  of  the 
bismuth  as  oxychloride,  BiOCl,  from  a  neutral  solution.  (An 
electrolytic  method  for  bismuth  with  lead  is  given  as  method  9.) 

For  the  detection  and  estimation  of  the  minute  quantities  of 
bismuth  present  in  refined  copper,  dissolve  50  to  100  grams  of 
the  drillings  in  175  to  350  c.c.  of  strong  nitric  acid,  diluted  with 
100  c.c.  of  water;  boil  the  liquid  and  add  a  little  more  hydro- 
chloric acid  than  the  amount  required  to  unite  with  the  silver. 
Dilute  the  solution  to  500  to  700  c.c.  and  add  ammonium  hy- 
droxide by  degrees  until  a  small  precipitate  of  copper  hydroxide 
remains  undissolved  after  stirring.  Allow  to  settle  in  a  warm 
place  overnight,  filter,  and  dissolve  the  precipitate  in  hot  15 
per  cent  nitric  acid.  Any  silver  chloride  will  remain  insoluble. 
If  much  is  present,  wash  it  from  the  paper  into  a  small  beaker 
and  boil  it  for  a  few  minutes  in  a  beaker  with  the  15  per  cent 
nitric  acid. 

Filter  through  the  original  paper  and  wash  with  hot  dilute 
nitric  acid.  The  liquid  should  be  quite  clear  except  when  con- 
siderable antimony  is  present.  If  the  liquid  is  clear,  evaporate 
it  to  dryness  on  the  steam  bath,  add  3  or  4  drops  of  hydrochloric 
acid  and  5  c.c.  of  water,  or  more  if-  required,  to  make  a  per- 
fectly clear  solution.  With  care,  a  solution  measuring  less  than 
10  c.c.  and  containing  only  2  or  3  drops  of  hydrochloric  acid  may 
be  obtained.  Dilute  this  slowly  with  water  to  150  c.c.,  thus 
precipitating  the  bismuth  slowly  as  BiOCl.  Since  the  oxychlo- 
ride  may  be  contaminated  with  a  little  copper,  redissolve  and 
precipitate  again  as  above. 

If  antimony  is  present,  the  first  precipitate  obtained  by 
ammonia  must  be  dissolved  in  dilute  hydrochloric  acid  and  the 


METHODS  FOR  FOREIGN  METALS   IN  COPPER          215 

metals  thrown  down  as  sulphides.  Filter,  and  boil  the  filter 
and  contents  with  dilute  potasfeium  hydroxide  and  sodium  sul- 
phide to  dissolve  any  antimony  cfr  arsenic.  Wash  the  insoluble 
sulphides  with  water  containing  a  little  of  the  same  reagent,  dis- 
solve them  in  nitric  acid,  and  proceed  as  before.  Filter  the 
purified  oxychloride  of  bismuth  on  a  small  asbestos  pad,  which 
has  been  thoroughly  extracted  with  acid,  dried,  and  weighed 
before  use.  Dry  the  filter  and  deposit  in  the  Gooch  crucible  at 
100°  to  105°  C.  and  weigh.  Dissolve  the  bismuth  compound 
in  hot  25  per  cent  hydrochloric  acid,  wash  the  pad  with  water, 
taking  care  that  no  fine  hairs  become  detached  in  the  operations; 
then  dry  and  weigh  again,  taking  the  weight  of  the  oxychloride 
by  difference. 

2.  Colorimetric  Method  (a).  —  The  original  process  of  F.  B. 
Stone1  has  been  somewhat  modified.  Dissolve  50  grams  of 
metal  in  200  c.c.  of  nitric  acid,  heat  to  expel  red  fumes,  and 
dilute  to  1000  c.c.  Add  a  small  crystal  of  ferric  sulphate,  or 
ferric  alum,  and  make  ammoniacal,  continuing  the  addition  with 
stirring  until  the  copper  hydroxide  redissolves.  Add  also  .75 
gram  of  pure  ammonium  carbonate  and  5  c.c.  of  sodium  phos- 
phate solution.  Heat  to  boiling  and  allow  to  settle  for  several 
hours  in  a  warm  place. 

Filter  off  the  precipitate,  wash  with  a  little  dilute  ammonia, 
and  dissolve  the  precipitate  in  a  little  hot  dilute  sulphuric  acid, 
preserving  the  filter  which  might  contain  a  trace  of  basic  chlo- 
ride. Dilute  the  solution  and  pass  hydrogen  sulphide  for  thirty 
minutes.  Filter  on  the  original  filter  and  wash  with  hydrogen 
sulphide  water.  Add  10  c.c.  of  a  saturated  solution  of  yellow 
ammonium  sulphide  and  warm  until  the  sulphides  are  dark  and 
the  supernatant  -liquid  clear.  (Potassium  hydroxide  with  a 
little  sodium  sulphide  may  be  used,  as  bismuth  sulphide  is 
slightly  soluble  in  the  sodium  compound,  alone.) 

Filter,  and  wash  with  the  alkaline  reagent,  much  diluted. 
Then  dissolve  the  insoluble  residue  by  boiling  with  dilute  15 
per  cent  nitric  acid,  and  separate  it  from  the  paper.  According 
to  F.  B.  Stone,  the  last  traces  of  copper  may  be  removed  by 
repeated  precipitation  with  ammonia  and  ammonium  carbonate. 
This  gives  results  which  are  a  little  too  low.  It  is  better 
to  make  slightly  alkaline,  then  add  a  little  pure  potassium 
1  Amer.  J.  Anal.  Chem.  1,  411. 


216  ANALYSIS  OF  COPPER 

cyanide  in  sufficient  amount  to  dissolve  the  copper  sulphide. 
Then  precipitate  the  bismuth  with  a  trace  of  lead  by  hydrogen 
sulphide. 

Filter  on  a  small  paper,  wash  thoroughly  with  hydrogen 
sulphide  water,  and  redissolve  in  a  little  hot  15  per  cent  nitric 
.acid.  Evaporate  to  fumes  with  .5  c.c.  of  sulphuric  acid,  dilute 
with  5  c.c.  of  water,  and  filter  into  a  test  tube,  or  colorimeter. 
Wash  the  filter  with  no  more  than  5  c.c.  of  dilute  sulphuric 
acid,  thereby  preventing  the  solution  of  any  lead  sulphate.  Add 
a  few  drops  of  a  10  per  cent  solution  of  pure  potassium  iodide, 
and,  afterwards,  a  few  drops  of  strong  sulphurous  acid  to  re- 
move any  trace  of  iodine  set  free  by  a  trace  of  ferric  sulphate. 

Finally,  compare  the  tint  of  the  liquid,  after  diluting  to  a 
known  mark,  with  measured  portions  of  a  standard  solution, 
which  have  been  similarly  treated  with  potassium  iodide  and 
sulphurous  acid.  One  c.c.  of  the  standard  contains  .0001  gram 
of  bismuth. 

Second  Option  (6) .  —  The  copper  may  be  removed  from  the 
sulphate  solution  by  alkaline  thiocyanate,  according  to  general 
method  1,  Chapter  XII.  When  this  method  has  been  used,  an 
aliquot  part  of  the  solution  is  clarified  by  filtration,  the  excess 
of  thiocyanate  and  sulphur  dioxide  removed  by  heating  and  add- 
ing a  little  nitric  acid,  and  the  bismuth  precipitated  by  hydrogen 
sulphide.  It  is  then  purified  from  traces  of  copper  and  lead 
sulphides  by  the  operations  already  described. 

IRON  AND   MANGANESE  IN  METALLIC   COPPER 

3.  Separation  from  Copper  by  Electrolysis.  —  Methods  1  to 
5  of  the  chapter  immediately  preceding  describe  the  treatment 
of  solutions  of  copper  containing  considerable  arsenic,  etc.,  up 
to  the  point  where  the  arsenic  and  associated  elements,  with  the 
last  traces  of  copper,  have  been  precipitated  by  hydrogen  sul- 
phide. The  filtrate  is  then  freed  from  hydrogen  sulphide  and 
most  of  the  sulphuric  acid  by  evaporation,  the  residue  dissolved, 
and  the  iron  and  associated  metals  determined  as  recommended 
in  the  following  paragraph. 

Dissolve  50  grams  of  clean  drillings,  strictly  free  from  dust, 
etc.,  in  a  750  c.c.  beaker  by  means  of  the  320  c.c.  of  the  "stand- 
ard acid  mixture"  adapted  for  the  electrolytic  assay  (Chapter 
XI).  The  acid  should  be  added  in  two  portions.  If  no  definite 


METHODS  FOR  FOREIGN  METALS  IN  COPPER         217 

acid  mixture  is  on  hand,  treat^  the  copper  with  250  c.c.  of  dis- 
tilled water,  80  c.c.  of  pure  sulghuric  acid  (d.,  1.84),  and  two 
portions  of  25  to  28  c.c.*  of  nitric  acid. 

Care  should  be  taken  that  the  first  acid  is  free  from  a  trace 
of  manganese.  C.  P.  sulphuric  acid  often  shows  this  impurity. 
A  careful  blank  analysis  of  all  the  reagents  and  distilled  water 
should  be  carried  along  with  each  set  of  copper  samples. 

The  solution  may  be  diluted  to  700  c.c.  and  electrolyzed  in 
the  large  Frary  solenoid,  described  in  Chapter  I,  or  the  ordinary 
cathode  may  be  combined  with  a  rotating  anode  of  platinum. 
If  necessary,  the  solution  may  be  washed  into  a  500  c.c.  beaker 
and  diluted  only  to  450  c.c.,  provided  that  the  current  is  started 
immediately  in  the  solenoid  to  prevent  crystallization.  The 
current  used  is  5  to  7  amperes  and  the  time  required,  seven  to 
fourteen  hours.  The  cathode  may  be  a  coarsely  perforated  plati- 
num cylinder,  11  cm.  in  height  and  7  cm.  in  diameter,  made  by 
bending  and  riveting  a  single  sheet.  A  narrow  double  seam  may 
be  formed  inside,  into  the  fold  of  which  a  wire  stem  is  inserted 
but  not  riveted.  As  soon  as  the  liquid  becomes  colorless,  wash 
down  the  glass  covers.  In  half  an  hour,  withdraw  the  electrodes, 
and  wash  them  with  water,  allowing  the  washings  to  drop  into 
the  electrolyte.  Evaporate  this  solution  rapidly  on  the  hot  plate, 
protecting  it  from  dust  byta  suspended  cover.  Transfer  the 
thick  sirupy  liquid  to  a  3a  porcelain  casserole  and  heat  strongly 
until  all  the  free  acids  and  most  of  the  acid  ammonium  sulphate 
are  expelled.  Dissolve  the  residue  in  10  drops  of  hydrochloric 
acid  and  50  c.c.  of  water,  then  saturate  the  solution  with  hydro- 
gen sulphide.  Filter,  wash  the  sulphides  with  water  containing 
hydrogen  sulphide,  heat  to  boiling,  and  recharge.  Reject  the 
precipitated  sulphides,  unless  antimony  is  to  be  determined 
according  to  methods  2  to  5,  Chapter  XII. 

Iron  and  Manganese.  —  Concentrate  the  filtrate  to  30  c.c., 
add  a  few  cubic  centimeters  of  bromine  water  to  complete  the 
oxidation,  then  boil  out  all  the  bromine  and  precipitate  the 
ferric  hydroxide  with  a  slight  excess  of  ammonia.  Filter,  re- 
dissolve  in  a  little  acid  and  water,  and  repeat  the  precipitation. 
Filter  on  an  ashless  filter,  wash  free  from  salts,  and  preserve 
both  filtrates  and  washings.  Some  of  the  best  sulphuric  acid 
contains  a  trace  of  manganese  which  interferes  with  the  nickel 
determination,  and  should  be  removed  with  the  ferric  hydroxide 


218  ANALYSIS  OF  COPPER 

by  adding  bromine  and  slight  excess  of  ammonia  and  heating. 
Remove  the  traces  of  manganese  from  the  ferric  hydroxide  by 
dissolving  and  precipitating  with  ammonia  alone  in  presence  of 
some  ammonium  chloride;  very  pure  ammonia,  free  from  iron 
and  pyridine,  should  be  used  for  this  work. 

COBALT,  NICKEL,  AND  ZINC 

Order  of  Determination.  —  The  elements  may  be  separated 
by  a  combination  of  accurate  European  methods,  similar  to  that 
published  by  R.  L.  Hallett.1  When  the  copper  contains  traces 
of  cobalt  with  much  nickel,  it  is  best  to  separate  the  cobalt 
first  by  the  process  of  Knorre  and  Illinski,  making  use  of  nitroso- 
l8-naphthol  (4).  The  determination  is  made  in  the  filtrate  from 
the  ferric  hydroxide.  The  filtrate  from  the  cobalt  is  evaporated 
to  fumes  with  sulphuric  acid,  cooled,  diluted  to  30  to  50  c.c., 
and  the  nickel  separated  by  dimethyl  glyoxime  (method  5). 
In  the  filtrate  from  the  nickel,  the  organic  reagent  is  destroyed 
by  evaporation  to  fumes  with  a  slight  excess  of  sulphuric  acid. 
The  zinc  is  then  precipitated. 

If  the  amount  of  cobalt  is  large  compared  with  the  nickel, 
reverse  the  order  of  separation.  In  most  of  the  brands  of  copper 
the  nickel  is  largely  in  excess,  however.  If  nickel  and  cobalt 
may  be  reported  together,  the  zinc  may  first  be  removed  by 
hydrogen  sulphide  (method  6),  filtered  off,  and  the  cobalt  and 
nickel  estimated  together  by  electrolysis. 

4.  Cobalt.  —  The  original  procedure  of  Knorre  and  Illinski 
has  been  modified.  To  separate  the  cobalt  from  the  nickel 
and  zinc,  acidify  the  filtrate  from  the  iron  precipitation  in 
the  first  method  with  hydrochloric  acid.  Evaporate  to  30  c.c. 
if  very  little  cobalt  is  present,  then  add  4  c.c.  of  hydrochloric 
acid  in  excess.  Warm,  and  add  a  hot  saturated  solution  of 
nitroso-/3-naphthol  in  50  per  cent  acetic  acid,  until  no  more  of 
the  cobalt  compound  [(Ci0H6O  —  NO)3Co]  is  formed.  After  a 
few  hours,  filter,  wash  first  with  cold  then  with  warm  12  per 
cent  hydrochloric  acid  until  the  nickel  salt  is  removed,  then 
with  hot  water  to  remove  all  the  acid.  Reduce  carefully  in  a 
Rose  crucible  with  oxalic  acid  in  a  current  of  hydrogen;  or 
ignite  in  a  platinum  crucible  to  oxide  of  cobalt,  Co3O4  (factor 
.7344).  A  third  method  is  more  accurate  than  either  form  of 
1  Eng.  and  Min.  Jour.  96,  857  (1913). 


METHODS  FOR  FOREIGN  METALS  IN  COPPER          219 

ignition.  Dissolve  the  red  salt  in  dilute  nitric  acid,  evaporate 
to  fumes  with  1  to  5  c.c.  of  sulphuric  acid,  dilute  to  30  c.c., 
make  strongly  alkaline  with  ammonia,  and  electrolyze  according 
to  the  conditions  specified  in  7. 

5.  Nickel.  —  The  delicate  reaction  with  dimethyl  glyoxime, 
discovered  by  Brunck  and  Tschugaeff,1  has  been  adapted  to  the 
analysis  of  copper.  If  the  nickel  is  to  be  determined  in  the 
filtrate  from  cobalt,  treat  the  filtrate  from  the  separation  in 
method  4  with  3  c.c.  of  sulphuric  acid,  evaporate  to  fumes,  and 
dilute  to  30  c.c. 

*  If  nickel  is  to  be  separated  first,  the  filtrate  from  the  iron 
precipitation  is  taken,  and  similarly  treated. 

Add  to  the  clear  acid  liquid  a  1  per  cent  alcoholic  solution 
of  dimethyl  glyoxime  in  amount  equal  to  nearly  five  times  the 
nickel,  and  make  the  solution  faintly  alkaline  with  ammonia. 
Solutions  from  high-grade  metal  may  be  rendered  alkaline  at 
once  and  any  trace  of  iron  filtered  out  before  the  special  reagent 
is  introduced.  Allow  to  stand  on  the  steam  plate  until  floccu- 
lent,  then  filter  while  hot  through  a  weighed  asbestos  felt  if  a 
direct  weight  of  the  salt  is  preferred.  Wash  with  hot  water 
containing  a  few  drops  of  ammonia,  and  dry  at  110  to  120°  C. 
to  a  constant  weight.  The  compound  (CsHuN^Ni)  contains 
20.325  per  cent  of  nickel,  Ni. 

Traces  of  nickel  may  be  weighed  more  accurately  by  dissolving 
the  red  salt  in  hot  (1 : 1)  hydrochloric  acid  without  previous 
drying.  Then  add  3  to  5  c.c.  of  sulphuric  acid  and  evaporate 
to  strong  fumes  of  sulphur  trioxide,  dilute  to  30  to  100  c.c. 
(according  to  the  amount  of  nickel  present),  and  add  30  per  cent 
by  volume  of  ammonia  (d.,  .90).  Electrolyze  as  in  method  7. 
It  may  prove  beneficial  with  high  nickel  to  add  15  c.c.  of  a 
saturated  solution  of  ammonium  carbonate  to  the  electrolyte. 

If  more  than  a  trace  of  zinc  or  cobalt  is  present,  as  in  alloys, 
or  scrap  metal,  it  may  be  necessary  to  redissolve  the  nickel 
oxime  in  a  little  hot  hydrochloric  acid  and  reprecipitate.  To 
recover  the  oxime  itself  for  further  use,  make  the  weighed  com- 
pound into  a  paste  with  a  little  water,  warm  it  with  potassium 
cyanide,  filter  hot,  and  precipitate  at  once  with  acetic  acid. 
Wash  and  dry  the  substance.  For  the  assay  of  nickel  in  crude 
material,  refer  to  Chapter  VII. 

1  Zeitsch.  Angew.  Chem.  20,  834  and  3844. 


220  ANALYSIS  OF  COPPER 

6.  Zinc,  —  With  Separation  of  Cobalt  and  Nickel.  —  Two  or 

three  brands  of  commercial  copper  contain  nickel  as  an  important 
constituent.  In  such  a  case,  the  organic  precipitates  obtained  by 
methods  2  and  3  are  too  voluminous  for  convenient  manipula- 
tion. In  the  assay  of  such  metal,  it  is  better  to  remove  the  zinc 
first  by  hydrogen  sulphide.  The  gas  is  expelled  from  the  filtrate 
and  the  nickel  and  cobalt  deposited  on  platinum.  In  routine 
work,  a  trace  of  zinc  would  be  deposited  and  weighed  with  the 
other  two  elements.  This  determination  is  made  on  the  filtrate 
from  the  iron  precipitation  of  method  3. 

When  a  separation  of  cobalt  and  nickel  has  already  been 
made  by  methods  4  and  5,  evaporate  the  last  filtrate  to  fumes 
with  3  c.c.  of  sulphuric  acid  to  destroy  the  organic  matter,  and 
dilute  to  25  c.c.  Make  slightly  alkaline  with  ammonia,  then 
faintly  acid  with  acetic  acid  or  formic  acid,  and  precipitate 
zinc  by  hydrogen  sulphide. 

In  order  to  separate  zinc  from  cobalt  and  nickel  in  solution, 
acidify  the  filtrate  from  the  iron  precipitation  (method  3)  with 
either  formic  or  glacial  acetic  acid,  then  add  an  excess  of  that 
acid  equal  to  one-sixth  of  the  volume  of  the  cold  solution. 
Saturate  the  cold  liquid  with  hydrogen  sulphide.  Allow  to  settle, 
filter,  test  again  with  the  gas  current,  and  filter.  Wash  the 
filters  with  hydrogen  sulphide  water  containing  a  little  ammo- 
nium acetate,  and  if  the  sulphide  is  not  white,  redissolve  and 
purify  it  from  a  trace  of  copper  or  lead.  Ignite  the  purified  sul- 
phide of  zinc  and  weigh  it  as  oxide,  containing  80.34  per  cent  of 
zinc.  "  Jena  glass  should  not  be  used  in  copper  analysis  as  it 
contains  soluble  zinc"  (Smoot).  t 

7.  Cobalt  and  Nickel  by  Electrolysis.  —  In  the  filtrate  from 
the  zinc  precipitation,  boil  out  every  trace  of  hydrogen  sulphide. 
Make  the  solution  ammoniacal  and  add  an  excess  of  ammonia 
(d.,  .90)  equal  to  30  to  40  per  cent  of  the  volume  of  the  solu- 
tion, which  should  have  a  final  volume  of  100  to  150  c.c.  for  .2 
gram  of  cobalt  or  nickel.     Better  results  are  obtained  if  the 
acetic  or  formic  acid  in  the  filtrate  from  zinc  is  destroyed  before 
electrolysis  by  evaporation  to  fumes  with   5   c.c.   of  sulphuric 
acid.     Cobalt  and   nickel  are  deposited  on  the  usual  type  of 
split  platinum  cylinders  in  ten  to  fourteen  hours  with  a  current 
of  .2  to  .5  ampere  at  a  potential  of  2.5  to  2.8  volts.     The  test 
for  the  end-point  is  made  by  treating  1   c.c.  of  the  electrolyte 


METHODS  FOR  FOREIGN  METALS  IN  COPPER         221 

on  a  porcelain  spot  plate  with  hydrogen  sulphide  water  or  alka- 
line sulphide.  Wash  the  cathode  finally  with  water  and  de- 
natured 90  to  94  per  cent  alcohol;  then  ignite  the  remainder  of 
the  alcohol  carefully  in  a  flame,  keeping  the  plate  in  rapid 
motion. 

The  revolving  anode,  or  the  Frary  solenoid,  permits  the 
deposition  to  be  completed  in  sixty  to  ninety  minutes  with  a 
current  of  3  to  4  amperes  per  square  decimeter  of  immersed  cath- 
ode surface  and  a  potential  of  5  volts.  When  cobalt  or  nickel  is 
separated  from  the  filtrates  in  methods  4  or  5,  a  trace  of  iron 
may  be  expected  from  impurity  in  the  organic  reagents.  In 
spite  of  the  ordinary  care  in  separations,  a  trace  of  copper  may 
also  be  present  in  the  deposited  metals. 

NOTE.  —  Smith  and  Lukens  have  proposed  to  deposit  cobalt 
as  dioxide  upon  a  platinized  platinum  anode  from  the  double 
fluoride  of  cobalt  and  ammonium  with  a  little  nitric  acid.  The 
separation  is  said  to  be  particularly  accurate  for  traces  of  the 
metal.  The  anode  deposit  is  ignited  to 


LEAD   IN  REFINED    COPPER 

8.  Author's  Method.2  —  Dissolve  20  grams  of  wire-bar  or 
casting  copper,  as  drillings,  in  100  c.c.  of  the  purest  nitric  acid 
(d.,  1.42),  evaporate  until  a  pellicle  forms,  and  dilute  to  500  c.c. 
with  distilled  water.  If  lower  grade  metal,  containing  more 
than  .01  per  cent  sulphur,  is  to  be  tested,  weigh  out  only  10 
grams  and  treat  with  60  c.c.  of  nitric  and  15  c.c.  of  hydrochloric 
acid.  Digest  with  fuming  nitric  acid  and  a  little  potassium 
chlorate  if  any  sulphur  remains  undissolved.  Evaporate  to 
a  sirup,  add  40  c.c.  of  nitric,  and  evaporate  again  until  a 
skin  begins  to  form.  Just  before  concentration,  drop  into  the 
beaker  .1  to  .5  gram  of  pure  sodium  carbonate,  or  sufficient 
to  unite  with  the  sulphur  present.  Finally,  neutralize  the  liquid 
with  ammonia  until  a  layer  of  copper  hydroxide,  about  3  mm. 
in  thickness  forms  on  the  bottom.  Place  the  beaker  in  a  large- 
size  Frary  solenoid  and  electrolyze  with  a  perforated  cathode 
measuring  10  cm.  in  diameter  and  about  11  cm.  in  height.  The 
anode  may  be  a  small,  closed,  perforated  cylinder  about  5  cm. 

1  Trans.  Am.  Electrochem.  Soc.  27  (1915),  30. 

2  J.  Am.  Chem.  Soc.  17,  814. 


222  ANALYSIS  OF  COPPER 

high  and  2  cm.  in  diameter,  provided  with  a  stem  of  heavy  wire, 
15  cm.  in  length.  Cover  the  beaker  with  split  glasses. 

Electrolysis  for  Lead.  —  Provide  a  slow  circulation  of  water 
in  the  narrow  annular  space  between  the  beaker  and  the  copper 
cylinder  which  forms  the  reel  for  the  insulated  wire  (see  Chapter 
I).  Commence  the  electrolysis  with  a  current  of  .5  ampere 
(ammeter  reading),  and  after  thirty  minutes  raise  the  current  to 
6  amperes  for  three  and  one-half  hours  additional.  At  the  end 
of  the  second  period,  the  lead  in  any  refined  copper  will  be 
entirely  deposited.  In  the  case  of  casting  copper  of  uncertain 
purity,  run  for  a  third  period  of  one  hour  with  a  second  clean 
anode  cylinder  in  order  to  obtain  the  last  trace  of  lead  as  dioxide. 
Remove  the  anode  very  quickly,  without  complete  interruption 
of  the  current;  plunge  it  into  a  little  beaker  of  distilled  water, 
'and  then  wash  it  carefully  with  a  jet  of  water.  Complete  the 
washing  with  denatured  alcohol  followed  by  ether,  and  finally 
dry  the  lead  deposit  in  a  hot-air  oven  for  fifteen  minutes  at 
200  to  230°  C. 

After  weighing  the  lead  dioxide  on  the  anode,  either  dissolve 
it  in  nitric  acid  containing  a  little  hydrogen  peroxide  or  a  few 
crystals  of  oxalic  acid,  or  immerse  it  in  cold  dilute  nitric  acid  in 
contact  with  a  strip  of  copper.  The  deposit  will  dissolve  in  a 
few  minutes.  Dry  and  weigh  the  plate  again.  It  is  incorrect 
to  weigh  the  anode  before  electrolysis  as  it  always  loses  a  little 
weight  during  the  operation. 

For  Lead  with  Bismuth.  —  A  trace  of  bismuth  oxide,  if  pres- 
ent in  solution,  may  deposit  with  the  dioxide  of  lead.  In  such 
a  case,  dissolve  the  peroxide  with  5  to  10  c.c.  of  a  mixture  of 
strong  nitric  and  oxalic  acids,  add  a  few  drops  of  sulphuric 
acid,  and  evaporate  to  fumes.  Dissolve  in  5  c.c.  of  water, 
filter  on  a  very  small  filter,  wash  with  a  few  drops  of  dilute 
sulphuric  acid,  and  test  the  filtrate  for  bismuth  by  method  2  of 
this  chapter. 

A  careful  test  should  always  be  made  for  a  trace  of  lead  in 
the  nitric  acid.  In  order  to  secure  the  same  conditions,  evapo- 
rate the  requisite  amount  of  nitric  acid  almost  to  dryness.  Add 
the  remaining  acid,  about  10  c.c.,  to  a  solution  of  20  grams  of  a 
high-grade  copper,  from  which  every  trace  of  lead  has  already 
been  removed  by  repeated  electrolysis.  Insert  electrodes  and 
pass  the  current  as  in  the  regular  analyses.  Any  traces  of 


METHODS  FOR  FOREIGN  METALS  IN  COPPER         223 

manganese  will  remain  in  solution.  Treat  the  weighed  anode 
with  the  reagent  to  dissolve  arty  lead,  then  wash,  dry  at  200°  C., 
and  weigh  again.  Deduct  the  arfcount  of  lead  oxide  obtained  in 
the  " blank"  from  the  result  of  the  analysis.  The  factor  required 
to  reduce  lead  dioxide  to  metallic  lead,  when  treated  as  described, 
has  been  determined  by  E.  F.  Smith  and  others  to  be  .8643. 

9.  Lead  —  First    Modification.  —  As   a   check  method  for 
minute  traces  of  lead,  A.  M.  Smoot  recommends  the  solution  of 
50  grams  of  the   borings  in  200   c.c.   of  nitric   acid  (d.,  1.42). 
Dilute  the  solution  to  700  c.c.  and  electrolyze  long  enough  to 
remove  the  lead,  employing  a  Frary  solenoid,  or  large  anode  and 
rotating  cathode.     Remove  the  anode  without  interrupting  all 
the  current,  and  wash  and  dry  as  in  the  first  modification  of  the 
electrolytic  method.     Dissolve  the  weighed  dioxide  of  lead  in  dilute 
nitric  acid  with  the  addition  of  a  few  drops  of  hydrogen  peroxide 
in   a   small   beaker.     Add  3  c.c.  of  sulphuric  acid  and  evapo- 
rate to  fumes.     Cool,  dilute  to  20  to  25  c.c.  with  water,  boil, 
and  allow  to  stand  overnight,  if  the  lead  is  to  be  weighed  as 
sulphate. 

The  sulphate  may  be  filtered  off,  dissolved  in  alkaline  tar- 
trate,  and  electrolysed  by  Dr.  Toisten's  formula  (10),  but  the 
author  considers  it  more  accurate  to  determine  the  traces  of 
oxides  of  manganese,  tin,  or  bismuth  which  may  be  present  in 
the  weighed  deposit  of  lead  dioxide,  and  deduct  the  observed 
correction.  In  the  determination  of  lead  in  bronze,  or  other 
copper  carrying  considerable  tin,  a  trace  of  stannic  oxide  may  be 
expected  in  the  lead.  When  the  amount  of  lead  is  known  to  be 
considerable,  it  is  advisable  to  interrupt  the  current  twice  for  a 
moment  or  two,  in  order  to  favor  the  resolution  of  any  trace  of 
lead  which  may  have  been  carried  over  on  the  cathode. 

10.  Deposition   as   Metallic   Lead.  —  Dr.    Toisten   separates 
small  amounts  of  bismuth  from  lead,  or  copper,  by  the  electrolysis 
of  a  hot  glucose,  or  sodium  tartrate  solution,  acidified  with  2  c.c. 
of  nitric  acid.     The  author  fails  to  obtain  any  good  separation, 
but  a  third  solution  recommended  for  the  deposition  of  considera- 
ble amounts  of  lead  as  metal  furnishes  very  good  results.     Lead 
nitrate,   dioxide,   or  sulphate   (after  separation  from  copper  by 
previous  methods),  is  dissolved  in  a  solution  containing  1  c.c.  of 
nitric  acid,  20  grams  of  tartaric  acid,  and  20  c.c.  of  concentrated 
ammonia.     Dilute  to  110  c.c.  and  electrolyze  at  a  boiling  heat 


224  ANALYSIS  OF  COPPER 

with  a  current  of  2  amperes  at  1.4  volts  potential.  With  an 
anode  revolving  800  to  1000  turns  per  minute,  the  deposition 
will  be  completed  in  ten  minutes  if  the  lead  weighs  less  than  .3 
gram.  The  deposit  on  the  cathode  is  washed,  dried  at  100°  C. 

or  less,  and  weighed. 

SULPHUR 

11.  Author's  Method  for  Refined  Copper.  —  After  the  lead 
has  been  removed  from  the  electrolyte  as  dioxide  (according  to 

8  or  9),  insert  a  clean  anode  wire  or  cylinder  in  the  beaker  of 
copper  solution,  prepared  from  a  20-gram  sample  of   drillings. 
Cover  the  beaker,  and  continue  the  electrolysis  with  a  current 
of  6  amperes,  or  4  amperes  overnight.     As  soon  as  the  liquid 
is  perfectly  colorless,  remove  and  wash  the  electrodes  into  the 
solution.    Concentrate  the  liquid  upon  a  plate  over  a  flame  which 
has  been  proved  to  be  free  from  sulphur  compounds.     Great  care 
must  be  taken  to  prevent  exposure  of  the  solutions  during  the 
analysis  to  fumes  of  hydrogen  sulphide,  or  sulphuric  acid.     In 
fact  the  operations  should  be  conducted  in  a  special  room,  if 
possible.     All  containers  should  be  rinsed  with  nitric  acid  and 
distilled  water  before  use. 

As  the  solution  concentrates,  transfer  it  gradually  to  a  7  or 

9  cm.  casserole,  and  remove  the  residual  ammonium  nitrate  by 
careful  evaporation  to  dry  ness  in  the  covered  dish  with  an  excess 
of  hydrochloric  acid.     Dissolve  the  salt  in  a  very  little  water 
and  evaporate  again  on  the  steam  plate  with  excess  of  hydro- 
chloric acid.     Repeat  the  operation.     If  a  trace  of  copper  was 
observed  in  the  first  residue  from  evaporation,  remove  it  entirely 
before  the  hydrochloric  acid  is  added,  by  electrolysis  in  small 
volume  with  a  narrow  platinum  strip.     Filter  the  pure  hydrochloric 
acid  solution  into  a  50  c.c.  lipped  beaker.     Then  heat  the  clear 
liquid  to  boiling,  add  3  to  5  c.c.  of  a  saturated  solution  of  barium 
chloride,  and  allow  to  stand  overnight.     The    solution    should 
contain  only  a  few  drops  of  acid.     Copper,  if  present  in  more 
than  traces,  retards  or  prevents  the  precipitation  of  traces  of 
barium    sulphate.     The   precipitation   may   be    completed   in   3 
hours  at  75°  C.     Filter  on  a  5  cm.  close,  washed  paper  and  ignite 
in  a  small  weighed  porcelain  crucible.     Barium  sulphate  (BaSO4) 
X  0.1373  =  Sulphur  (S). 

Modification  for   Converter,    or   Blister   Copper.  —  Dissolve   a 
5-gram  sample  in  a  sufficient  amount  of  nitric  acid  mixed  with 


METHODS  FOR  FOREIGN  METALS  IN  COPPER         225 

hydrochloric  to  oxidize  the  sulphur  without  the  formation  of 
globules.  Evaporate  the  solution  repeatedly  with  nitric  acid 
until  the  hydrochloric  acid  is  rerrioved.  Filter  off  any  insoluble 
matter,  wash,  and  boil  the  residue  with  a  few  cubic  centimeters 
of  a  saturated  solution  of  sodium  carbonate,  in  order  to  convert 
any  trace  of  lead  sulphate  to  carbonate  and  form  a  soluble  sul- 
phate. Filter  off  any  insoluble  matter,  wash  once,  and  evaporate 
to  dryness  with  an  excess  of  hydrochloric  acid.  Dilute  until 
the  residue  dissolves  and  test  for  a  trace  of  sulphates  by  barium 
chloride. 

Electrolyze  the  copper  solution  and  conduct  the  remainder  of 
the  test  as  directed  in  the  method  for  refined  copper.  A  little 
potassium  chlorate  or  bromine  will  also  be  required  to  oxidize 
all  the  sulphur  in  crude  metal. 

DEOXIDIZING  ELEMENTS 

12.  Aluminum,  Boron,  Manganese,  or  Phosphorus.  —  These 
seldom  occur  in  any  commercial  copper  unless  added  in  some 
special  crucible  treatment  in  the  foundry.  The  determination  of 
these  elements  in  quantity  is  described  in  the  next  chapter. 
Small  amounts  of  these  elements,  which  have  been  added  as 
deoxidizers,  may  be  detected  as  follows  : 

Electrolyze  a  nitric  acid  solution  of  the  copper  drillings  in 
the  same  manner  as  for  the  lead  determination.  Test  the  anode 
deposit  for  manganese,  or  simply  dissolve  any  slight  deposit  and 
return  it  to  the  solution.  Evaporate  the  solution  to  dryness 
to  test  for  manganese.  A  complete  deposition  of  traces  of 
manganese  on  an  anode  can  only  be  obtained  from  a  sulphate 
solution  of  small  volume.  To  obtain  phosphorus  from  the 
electrolyte,  concentrate  to  a  small  volume  and  precipitate  by 
ammonium  molybdate  from  the  hot  solution,  according  to 
methods  of  iron  analysis. 

Lucien  Robn  states  that  minute  traces  of  boron  may  be 
detected  in  solution  by  the  addition  of  tincture  of  mimosa 
blossoms.1  Determine  according  to  Fresenius.2  Aluminum  will 
be  precipitated  as  hydroxide  with  the  iron  (in  the  determination 
of  iron),  and  may  be  separated  therefrom  by  the  methods  adopted 
for  alumina  in  slags,  Chapter  V. 

1  Proc.  8th  Inter.  Congress  of  Appl  Chem.  1,  429.  2  Quant.  Anal. 


226  ANALYSIS  OF  COPPER 

OXYGEN  AND   OCCLUDED   GASES 

13.  By  Ignition  in  Carbon  Monoxide.  —  Mr.  T.  West  has 
proposed   to    heat    copper,    or   brass,    in   but   one    gas,    carbon 
monoxide,  CO.     A  high  heat  must  be  maintained  to  obtain  any 
quantitative  reduction,  and  as  yet  the  writer  has  not  succeeded 
very  well  with  this  operation.     The  temperature  recommended 
is  900°  C.  for  copper  and  up  to  1050°  for  brass,  the  time  varying 
between  two  and  three  hours.      It  is  claimed  that,  in  spite  of 
the  volatility  of  zinc,   the  oxides  may  now  be  determined  in 
brass.     The    zinc   is    condensed    in    special    apparatus    and    the 
carbon  dioxide  is  absorbed  and  weighed.     The  carbon  monoxide 
may  be  generated  by  the  method  given  in  Chapter  III,  and  must 
be  purified  from  carbon  dioxide  and  oxygen. 

14.  Author's  Method,  —  Ignition   in   Hydrogen   and  Carbon 
Dioxide.  —  Dr.   Hampe1   first   proposed  that   oxides  in    copper 
should  be  accurately  determined  by  the  loss  of  weight  sustained 
by  finely  divided  copper  when  reduced  in  pure  hydrogen,  or  by 
the  weight   of  water  produced.     The   author  has  proved   that 
additional  precautions  must  be  taken  to  correct  for  certain  errors 
inherent  in  the  original  method. 

First:  —  Traces  of  sulphur  are  evolved,  and  when  accurate 
results  are  desired,  the  hydrogen  sulphide  should  be  absorbed  in 
ammoniacal  cadmium  chloride,  and  the  trace  of  sulphur  de- 
termined by  titration  with  iodine,  and  deducted  from  the 
apparent  loss  of  the  copper. 

Second: — The  apparent  loss  of  the  copper  when  heated  in  hy- 
drogen to  constant  weight,  includes  a  trace  of  occluded  gases,  and 
occasionally  moisture,  present  in  the  original  metal.  These  may 
be  expelled  by  a  preliminary  heating  in  carbon  dioxide,  although 
the  quantity  is  so  small  as  to  be  negligible  in  ordinary  work. 
The  water  formed  may  be  weighed  and  one-ninth  of  the  weight 
taken  as  "occluded  gas,"  because  the  gas  is  principally  hydrogen. 

Third:  —  About  .01  .per  cent  of  hydrogen  by  weight  is  re- 
tained by  the  copper  after  reduction  in  a  current  of  hydrogen 
at  a  red  heat.  This  error  has  already  been  noted  and  corrected 
in  the  author's  modification.2  Since  copper  has  practically  no 
affinity  for  carbon  dioxide,  a  subsequent  heating  for  twenty 

1  Z.  fur  Berg  Hiitten  und  Salinen  Wesen,  1873, 

2  /.  Ind.  and  Eng.  Chem.,  4  (1912),  402. 


METHODS  FOR  FOREIGN  METALS  IN  COPPER          227 

minutes  in  the  latter  gas  will  expel  the  remaining  hydrogen. 
The  carbon  dioxide  is  finally  expelled  by  dry  air  after  cooling. 
" Over-poled"  copper  contains  ifiore  gas  than  metal  of  lower 

pitch. 

METHOD 

Preparation  of  the  Copper  for  Ignition.  —  In  exceptional  cases, 
it  may  be  necessary  to  dry  a  sample  of  porous  metal  at  100°  C. 
in  an  atmosphere  of  pure  nitrogen,  or  carbon  dioxide.  Any  oil 
may  be  removed  from  drillings  by  ether.  Samples  should  be 
taken  with  a  clean  drill,  and  the  speed  and  diameter  regulated 
to  produce  small  chips,  free  from  any  trace  of  oxidation  by  heat- 
ing. A  fair  sample  may  be  obtained  from  a  casting  by  observ- 
ance of  the  " copper  specifications"  of  the  American  Society  for 
Testing  Materials.  In  order,  however,  to  measure  the  exact 
relation  between  the  copper  and  oxygen  in  a  sample,  it  is 
necessary  to  determine  the  oxygen  on  the  same  bottle  of  fresh 
drillings  that  is  used  for  the  estimation  of  copper  and  silver  by 
electrolysis.  The  oxygen  varies  inversely  as  the  copper  content 
of  a  casting,  and  although  .005  to  .01  per  cent  may  be  a  good 
check  in  electrolysis,  it  constitutes  a  large  percentage  error  in 
an  oxygen  determination. 

A.  M.  Smoot  notes  that  it  is  almost  impossible  to  remove 
all  the  soapy  lubricant  from  some  drawn  wires  by  direct  washing 
with  alcohol  or  ether.  Such  material  may  be  cut  in  short  pieces 
and  digested  for  a  few  minutes  with  a  1  per  cent  solution  of 
potassium  hydroxide  in  alcohol,  having  the  liquid  warm  but  not 
hot  enough  to  oxidize  the  metal.  Finally,  wash  with  water, 
alcohol,  and  ether,  in  rapid  succession.  If  a  slight  abrasion  of 
the  "skin"  of  the  wire  is  not  objectionable,  the  wire  may  be 
scoured  with  wet  sharp  silica,  which  has  been  ground  to  pass 
through  a  sieve  of  40  meshes  to  the  linear  inch.  The  wire  may 
then  be  cut  up,  treated  with  alcohol  and  ether,  and  dried  off  at 
a  low  heat. 

Preparation  of  Pure  Carbon  Dioxide.  —  A  pure  gas  for  re- 
search may  be  prepared  by  the  method  of  Bradley  and  Hale,1  who 
generate  the  gas  by  the  action  of  strong  sulphuric  acid  on  a 
paste  of  sodium  bicarbonate  and  water.  This  process  requires 
too  much  apparatus  and  attention  for  technical  analysis. 
Carbon  dioxide  of  sufficient  purity  may  be  generated  from  pure 
1  J.  Am.  Chem.  Soc.  30,  1090. 


228  ANALYSIS  OF  COPPER 

white  lump  marble,  or  calcite,  provided  that  proper  reagents  are 
used  to  absorb  the  traces  of  oxygen  and  hydrocarbons  which  are 
continuously  evolved.  A  trace  of  oxygen  in  the  carbon  dioxide 
or  hydrogen  will  produce  a  dark  tint  on  the  hot  reduced  metal 
at  the  point  where  the  gas  enters  the  bulb. 

The  purification  train  of  tubes  is  arranged  in  order  as  follows : 
(a)  Casamajor  or  small  Kipp  generator  with  an  elevated  pressure 
bottle.  The  apparatus  should  be  small  enough  to  permit  the 
expulsion  of  every  trace  of  air  in  thirty  minutes'  evolution  before 
the  gas  is  passed  over  the  copper.  (6)  Bulb  containing  a  satu- 
rated solution  of  mercuric  chloride  for  the  absorption  of  hydro- 
carbons, (c)  A  glass  tube  containing  a  saturated  solution  of 
silver  sulphate  in  dilute  sulphuric  acid,  (d)  A  Bowen's  potash 
bulb  with  strong  sulphuric  acid,  (e)  A  preheating  tube  for 
removal  of  traces  of  oxygen.  This  consists  of  a  25  cm.  ignition 
tube  in  which  is  tightly  fitted  a  15  cm.  roll  of  copper  gauze. 
The  tube  is  heated  to  a  low  red  heat  by  two  fish-tail  burners, 
but  the  gas  should  not  be  lighted  until  the  air  has  been  driven 
out  of  the  bottle  and  tubes,  to  prevent  rapid  oxidation  and 
deterioration  of  the  copper.  This  gauze  may  be  regenerated  in 
fifteen  minutes  by.  reversing  the  valves  and  passing  hydrogen 
from  the  companion  generator.  (/)  Last  in  the  gas  train  are 
two  drying  tubes  filled  with  strong  sulphuric  acid  or  phosphoric 
anhydride  as  preferred.  The  phosphoric  anhydride  is  opened  up 
with  glass  wool,  (g)  The  train  from  this  generator  and  the  one 
producing  hydrogen  are  finally  connected  to  each  arm  of  a  glass 
tee,  provided  with  two  three-way  valves.  The  valve  from  the 
carbon  dioxide  bottle  is  arranged  to  discharge  into  the  air  for 
thirty  minutes  before  the  gas  is  used  in  order  to  remove  the  last 
traces  of  oxygen.  After  the  three-way  valve  is  placed  a  hard 
glass  tube  one  foot  in  length,  having  one  large  bulb  or  two  of 
smaller  size.  A  silica  tube  with  porcelain  or  alundum  boats  may 
also  be  used  to  hold  the  50-  or  100-gram  sample  of  fine  copper 
drillings. 

Preparation  of  Pure  Hydrogen.  —  This  generator  should  also 
be  of  rather  small  size  in  order  that  the  air  may  be  quickly 
swept  out.  The  gas  may  be  more  easily  purified  if  it  is  gener- 
ated from  pure  zinc  and  dilute  sulphuric,  instead  of  hydrochloric 
acid.  In  accordance  with  a  suggestion  of  A.  M.  Smoot,  one  drop 
of  a  10  per  cent  solution  of  platinic  chloride  is  added  to  two 


METHODS  FOR  FOREIGN  METALS  IN  COPPER         229 

liters  of  (1:4)  sulphuric  acid,  ^his  trace  of  platinum  promotes 
a  steady  flow  of  gas.  Good  hydrogen  may,  of  course,  be  pur- 
chased, if  preferred.  T^ie  purifying  train  consists  of :  (a)  The 
generator  or  gas  cylinder;  (b)  Allihn  washing  bottle  containing 
a  10  per  cent  solution  of  potassium  hydroxide,  saturated  with 
potassium  permanganate;  (c)  tubes  for  the  removal  of  traces 
of  oxygen,  in  which  there  is  a  choice  of  three  alternatives,  the 
first  being  preferred.  The  first  is  an  Allihn  250  c.c.  bottle  of 
potassium  hydroxide  solution  (d.,  1.27)  in  which  is  dissolved  5 
grams  of  pyrogallic  acid;  second,  a  heated  tube  of  5  per  cent 
palladium  asbestos;  or  third,  a  tube  containing  a  long  roll  of 
reduced  copper  gauze  or  turnings,  heated  in  a  short  furnace. 
(d)  Two  tubes  of  drying  reagent  follow.  The  same  reagents 


Cd  C/* 

Fig.  16.  —  Section  of  Apparatus   for  Estimation  of  Oxygen  in  Copper. 

should  be  placed  before  the  copper  to  dry  the  gas  that  are 
placed  after  the  ignition  tube  to  catch  any  evolved  moisture  for 
weighing.  Bulbs  of  strong  sulphuric  acid  are  efficient,  or  glass- 
stoppered  tubes  of  phosphoric  anhydride  mixed  with  glass  wool. 
The  general  custom  has  been  to  determine  the  oxygen  by  the 
loss  in  weight  of  the  copper  sample.  The  gas  passing  over  the 
red-hot  drillings  is  passed  through  a  small  U  tube  or  bottle 
containing  10  c.c.  of  a  2  per  cent  solution  of  ammoniacal  cad- 
mium chloride  in  order  to  absorb  traces  of  evolved  sulphur. 
By  a  combination  of  tubes,  the  water  may  also  be  weighed. 

Ignition.  —  The  reduction  may  be  made  in  a  hard-glass  tube 
about  30  cm.  long  and  6  mm.  internal  diameter,  provided  with 
one  large,  or  two  small  central  bulbs.  The  tube  is  placed  on  a 
lamp  ring  of  10  cm.  diameter  and  is  protected  from  over-heating 
by  wrapping  it  with  a  piece  of  asbestos  paper,  clamped  with  a 
loop  of  stiff  wire.  The  estimation  of  the  oxygen  by  simple  loss 
in  weight,  without  corrections,  is  rapid  but  approximate.  For 


230  ANALYSIS  OF  COPPER 

such  a  test,  four  samples  of  20  grams  each  may  be  placed  in 
weighed  boats  in  a  combustion  tube  heated  by  an  ordinary  gas 
furnace.  The  electric  furnaces  adopted  for  carbon  in  steel  are 
efficient  but  heat  very  slowly. 

Analysis.  —  Clean,  ignite,  and  weigh  the  tube  or  boat  to  be 
used.  Weigh  about  50  grams  of  the  fine  clean  drillings,  or  filings, 
and  feed  them  into  the  central  bulb  of  the  tube  by  stopping  one 
end  with  a  glass  rod,  and  using  at  the  opposite  end  a  short 
funnel,  into  which  the  drillings  may  be  fed  with  the  aid  of  a 
stiff  wire.  After  the  material  has  been  packed  by  tapping,  the 
tube  should  be  wiped  dry  with  a  warm  cloth,  and  allowed  to 
stand  on  the  balance  for  ten  minutes  before  weighing.  Connect 
the  bulb  tube  to  the  gas  apparatus  and  make  sure  that  the 
joints  are  all  tight.  Pass  pure  carbon  dioxide  through  the  cold 
tube  for  thirty  minutes,  if  occluded  gases  are  to  be  investigated. 

Occluded  Gases.  —  If  some  knowledge  of  the  gases  is  desired, 
heat  the  bulb  tube  to  a  red  heat  for  twenty  minutes  in  the 
current  of  carbon  dioxide.  The  bulbs  should  be  protected  by 
wrapping  with  asbestos  paper  held  in  place  with  a  stout  wire. 
Three  Bunsen  burners  give  sufficient  heat.  The  tube  is  then 
cooled  by  an  air  blast,  the  carbon  dioxide  finally  being  expelled 
by  the  passage  of  a  current  of  dry  air  for  ten  minutes.  Wipe 
the  tube  clean  and  allow  to  stand  in  the  balance  ten  minutes 
before  taking  the  .final  weight  to  determine  the  loss  in  ignition. 
One-ninth  of  the  loss  expresses  approximately  the  original  gas, 
as  it  is  principally  hydrogen,  and  would  abstract  oxygen  from 
the  copper  to  form  water  vapor.  For  the  purposes  of  analysis, 
it  is  sufficiently  accurate  to  omit  this  ignition  in  carbon  dioxide, 
and  ignite  in  hydrogen  at  once.  (The  tube  used  by  Dr.  H.  O. 
Hofman  will  contain  100  grams  of  copper.) 

Oxygen.  —  Connect  the  drying  bulbs  with  the  copper  sample 
tube  and  attach  a  U  tube  containing  10  c.c.  of  the  ammoniacal 
solution  of  cadmium  chloride.  Pass  a  current  of  pure  hydrogen 
through  the  cold  tube  for  fifteen  minutes  at  the  rate  of  one  large 
bubble,  or  four  small  ones,  per  second,  in  order  to  expel  all  the 
air.  Now  raise  the  tube  to  a  good  red  heat  by  a  furnace  or 
triple  burner,  and  maintain  the  temperature  below  the  point 
which  would  cause  the  metal  to  distil  into  the  glass.  Heat  one 
hour  if  the  sample  is  reduced  to  filings,  or  two  hours  for  fine 
drillings.  The  necessary  time  should  be  determined  by  experi- 


METHODS  FOR  FOREIGN  METALS  IN  COPPER         231 

ment  for  drillings  of  the  size  to  be  tested.  Twenty  to  thirty 
minutes  before  the  reduction  in  hydrogen  is  completed,  the 
carbon  dioxide  generator-  should  T>e  started,  as  already  directed, 
and  allowed  to  discharge  into  the  air  at  the  three-way  valve. 
A  quick  turn  of  two  glass  valves  will  then  substitute  carbon 
dioxide  for  hydrogen,  and  twenty  minutes  additional  heating 
in  the  carbon  dioxide  will  expel  the  hydrogen  (about  .01  per 
cent)  which  would  otherwise  have  been  retained  by  the  copper. 
Cool  in  the  current  of  carbon  dioxide  for  ten  minutes,  using  a 
small  air  blast,  and  then  replace  the  gas  by  dry  air  from  a  pipe 
attached  temporarily  to  the  three-way  valve.  Place  in  the 
balance  and  weigh  in  ten  minutes. 

To  determine  the  correction  for  the  traces  of  sulphur  evolved, 
place  70  c.c.  of  water  in  a  tall  No.  1  beaker,  and  transfer  the 
cadmium  solution  and  sulphide  as  rapidly  as  possible  with 
the .  aid  of  30  c.c.  of  (1  :  1)  hydrochloric  acid.  Titrate  at 
once  with  standard  iodine.  If  2  grams  of  iodine  are  dissolved 
in  one  liter  of  water,  1  c.c.  will  equal  .00025  gram  of  sulphur. 
Deduct  the  weight  of  sulphur  from  the  apparent  loss  of  weight 
of  the  copper,  and  the  result  will  express  the  weight  of  oxygen 
in  the  metal. 

A  check,  or  experimental  proof  of  the  completeness  of  the 
reduction,  may  be  obtained  by  a  careful  electrolytic  assay  of  the 
reduced  drillings  from  the  tube,  correcting  the  assay  for  the  trace 
of  copper  in  electrolyte. 

Rapid  Method.  —  In  routine  work,  results  may  be  obtained 
in  quicker  time  by  heating  several  samples  in  one  tube  in  por- 
celain boats  for  two  hours.  If  cooled  in  hydrogen  (after  Cobel- 
dick),  the  method  is  more  rapid,  but  approximate.  If  finally 
heated  and  cooled  in  carbon  dioxide,  as  recommended  by  the 
author,  the  only  appreciable  error  is  that  due  to  the  loss  of  a 
trace  of  sulphur. 

15.  Photo-micrographic  Method.  —  Following  Heyn,1  and 
the  work  of  Hofman,  Green  &  Yerxa2  in  the  measurement  of 
a  microscopic  field  with  a  planimeter,  E.  S.  Bardwell3  projects 
the  area  of  the  microscopic  field  directly  upon  a  piece  of  duplex 
paper  in  a  16-inch  circle,  and  then  traces  and  cuts  out  the 
copper  areas,  leaving  a  net-work  of  paper,  representing  the  eu- 

1  Mittheil.  aus  den  Konigl.  Versuchtsanstalten  zu  Berlin  18,  315. 

2  Trans.  A.  I.  M.  E.  34,  671.  3  Ibid.  Bull.  79  (1913),  1429. 


232  ANALYSIS  OF  COPPER 

tectic.  The  two  lots  of  paper  are  carefully  weighed  and  the 
weights  are  proportional  to  the  areas  of  copper  and  eutectic 
(Cu  +  Cii20  containing  3.45  per  cent  Cu2O). 

The  polished  copper  is  etched  by  heating  it  for  three  or  four 
minutes  in  a  current  of  hydrogen  gas  at  about  300°  C.,  or  low 
red  heat,  first  passing  the  gas  for  ten  minutes  to  drive  out  the 
air.  This  scheme  can  only  be  approximate  in  the  case  of  cast 
copper  because  there  is  so  much  variation  in  the  crystalline 
aggregates,  and  it  requires  about  as  much  time  per  sample  as  the 
rapid  method  already  described  in  14. 

TIN  IN  COPPER 

16.  Special  Method.  —  The  separation  of  tin  from  antimony 
or  arsenic  has  been  described  (10,  Chapter  XII).  Copper  refined 
from  foundry  scrap,  or  from  metal  which  may  have  been  elec- 
trolyzed  with  lead  anodes,  will  occasionally  contain  a  trace  of  tin. 
The  following  is  developed  from  the  method  of  W.  H.  Bassett, 
devised  for  this  material. 

Dissolve  two  portions  of  75  to  100  grams  each  in  500  c.c.  of 
distilled  water  and  250  to  300  c.c.  of  pure,  strong  nitric  acid. 
The  distilled  water  employed  should  not  be  distilled  from  a  tin- 
lined  condenser.  After  the  acid  has  been  added  gradually  and 
the  copper  has  dissolved,  boil  the  solutions  down  to  a  sirup. 
When  a  skin  begins  to  form  on  the  surface,  cool  slightly,  dilute 
with  a  few  cubic  centimeters  of  nitric  acid  and  600  c.c.  of  water, 
and  heat  until  all  is  dissolved.  If  a  little  basic  copper  remains, 
add  a  very  little  acid  until  it  clears  up,  and  allow  to  stand  on 
the  steam  plate  for  at  least  two  hours  but  better  overnight. 
The  solution  should  not  be  allowed  to  cool  until  it  is  filtered. 
Pass  both  solutions  through  the  same  small  doubled  filter, 
reserving  all  insoluble  residue  until  the  last.  Remove  the 
large  beaker  and  replace  by  a  small  clean  beaker,  then  trans- 
fer the  residue  to  the  filter.  The  precipitate  may  contain  a 
trace  of  iron  and  phosphate  of  tin,  also  a  part  of  the  antimony 
present.  It  may  be  purified  by  the  method  used  in  the 
analysis  of  bronze,  Chapter  XIV.  Dissolve  the  tin  oxide, 
etc.,  in  a  little  yellow  ammonium  sulphide  containing  about  3 
per  cent  of  pure  ammonium  chloride.  Filter,  precipitate  the 
tin  with  a  slight  excess  of  acetic  acid,  and  filter  again.  Wash 
with  water  acidified  with  acetic  acid,  and  ignite  carefully  to 


METHODS  FOR  FOREIGN  METALS  IN   COPPER         233 

oxide    with    the    precautions    noted    in    Fresenius'    Quantitative 
Analysis. 

SELENIUM  AND  ^TELLURIUM 

17.  Special  Method.  —  The  rapid  combination  method  of  the 
author  for  the  estimation  of  the  two  elements,  in  connection 
with  the  arsenic  and  antimony,  has  already  been  described  (7, 
Chapter  XII),  and  is  recommended.  The  papers  of  E.  Keller1 
and  C.  Whitehead2  present  two  original  schemes  which  are 
slower,  but  are  capable  of  equally  good  results.  The  elements 
are  separated  by  excess  of  ferric  hydroxide.  The  copper  must  be 
completely  removed  by  repeated  treatment,  or  a  loss  will  result 
when  the  ferric  hydroxide  is  finally  dissolved  in  acid  and  the 
solution  treated  with  hydrogen  sulphide.  If  any  silver,  or 
copper,  is  present,  some  silver  or  copper  selenide  may  be  formed, 
which  is  afterwards  insoluble  in  alkaline  sulphides.  Proceed  as 
in  the  next  paragraph. 

Dissolve  two  portions  of  50  grams  of  refined  copper  in  sepa- 
rate beakers,  using  in  each  case  200  c.c.  of  nitric  acid  (d.,  1.42), 
of  tested  purity.  Add  to  each  30  c.c.  of  a  10  per  cent  solution 
of  ferric  ammonium  sulphate,  or  2  grams  of  ferric  nitrate,  render 
sufficiently  ammoniacal  to  redissolve  all  the  copper  hydroxide 
formed,  then  heat  to  boiling  and  allow  to  settle.  Filter,  wash 
with  dilute  ammonia,  wash  most  of  the  ferric  hydroxide  into  the 
original  beaker,  and  dissolve  in  (1  : 20)  sulphuric  acid  with  a 
little  hydrochloric.  Precipitate  again  and  filter  on  the  same 
filter.  Repeat  the  operations  until  the  filtrate  shows  no  blue 
color  of  copper.  Finally,  dissolve  the  hydroxide  in  the  least 
possible  amount  of  hydrochloric  acid  diluted  with  10  volumes  of 
water.  From  this  point,  there  are  two  or  three  separations  which 
are  a  matter  of  individual  preference. 

(a)  Modification  of  E.  Keller.  —  Saturate  the  cold  hydro- 
chloric acid  solution  of  the  ferric  hydroxide,  etc.,  with  hydrogen 
sulphide  gas.  Copper  must  be  absent  and  the  solution  must  be 
cold  to  render  the  selenium  sulphide  soluble  in  sodium  sulphide. 
Filter,  wash,  and  digest  with  a  little  sodium  sulphide  solution. 
Filter  off  insoluble  matter,  wash  the  filter,  acidify  the  solution 
with  nitric  acid,  and  evaporate  to  dryness.  The  latter  operation 
must  be  performed  with  care  on  the  water  bath  or  steam  plate. 
If  five  drops  of  sulphuric  acid  are  added  during  concentration,  no 
1  J.  Am.  Chem.  Soc.  22,  242.  2  /^  17>  280. 


234  ANALYSIS  OF  COPPER 

nitric  acid  will  remain  in  the  residue.  To  this  residue  add  180 
c.c.  of  hydrochloric  acid  (d.,  1.2)  and  20  c.c.  of  water.  Boil 
just  long  enough  "to  destroy  any  nitrous  compounds  and  reduce 
selenium  and  tellurium  to  the  lower  chlorides.  If  the  salts  are 
not  excessive,  90  c.c.  of  acid  with  10  c.c.  of  water  are  sufficient, 
and,  if  the  sulphuric  acid  was  added  exactly  to  replace  the 
nitric,  it  is  better  to  heat  just  to  boiling  and  then  remove  to 
prevent  loss  of  selenium.  Cool  the  solution  and  filter  out  any 
sulphur  or  insoluble  halide  through  an  asbestos  felt  on  a  Gooch 
crucible.  Wash  the  residue  several  times  with  90  per  cent 
hydrochloric  acid.  The  filtrate  is  now  ready  for  saturation  with 
sulphur  dioxide  gas,  which  may  be  supplied  from  a  steel  cylinder, 
or  generated  by  copper  borings  and  acid. 

The  author  prepares  the  sulphur  dioxide  more  easily  from  a 
solution  of  sodium  sulphite  which  is  allowed  to  drop  into  strong 
sulphuric  acid  (Chapter  III).  Charge  the  hot  solution  with  the 
gas,  allow  to  cool  while  charging,  and  set  the  beakers  away  until 
the  precipitate  has  settled.  Filter  the  selenium  on  a  weighed 
Gooch  felt  and  wash  three  times  with  90  per  cent  hydrochloric 
acid.  Set  the  filtrate  aside  and  wash  the  selenium  free  from 
salts  by  successive  treatment  with  dilute  hydrochloric  acid, 
water,  and  strong  alcohol.  Dry  at  100  to  105°  C.  for  one  hour, 
cool,  and  weigh  immediately.  Saturate  the  solution  with  the 
sulphur  dioxide  a  second  time  to  be  sure  of  complete  precipitation. 

The  filtrate  from  the  second  precipitation  contains  the  tel- 
lurium. Add  water  to  double  the  volume,  then  boil  the  solution 
for  several  minutes,  while  sulphur  dioxide  is  again  conducted 
through  the  liquid.  Filter  when  cooled,  wash,  dry,  and  weigh 
as  before.  The  felts  containing  both  selenium  and  tellurium 
may  be  ignited  to  drive  off  the  two.  elements,  and  the  felts 
reweighed  as  a  check.  With  some  asbestos,  there  is  a  notable 
difference  between  the  ignited  weight  and  the  weight  after 
moistening  the  ignited  felt  and  drying  in  an  oven  at  105°  C. 
The  latter  weight  corresponds  to  the  original  dried  weight  of 
the  felt. 

(6)  Modification  of  C.  Whitehead,  —  The  preceding  method  is 
exactly  followed  until  the  solution  of  ferric  hydroxide  has  been 
obtained,  strictly  free  from  copper  salts.  Add  1  gram  of  solid 
tartaric  acid,  make  alkaline  with  an  excess  of  potassium  hydrox- 
ide, and  pass  hydrogen  sulphide  gas  into  the  solution  for  thirty 


METHODS  FOR  FOREIGN  METALS  IN  COPPER         235 

minutes.  Filter,  decompose  the  sulphides  of  selenium  and 
tellurium  with  dilute  hydrochloric  acid  and  allow  the  liquid  to 
stand  in  a  warm  place  until  tfe  hydrogen  sulphide  is  removed. 
Filter  again,  dissolve  the  sulphides  in  aqua-regia  (nitric  and 
hydrochloric  acids),  add  .2  gram  of  potassium  chloride,  and 
evaporate  the  liquid  to  dryness  on  the  steam  plate.  Take 
up  with  90  per  cent  hydrochloric  acid,  heat  to  boiling,  and 
precipitate  with  sulphur  dioxide  as  in  the  first  modification. 

(c)  Precipitation  by  Stannous  Chloride.  —  When  the  selenium 
is  largely  in  excess,  a  fairly  good  separation  is  most  easily 
obtained  by  adding  an  excess  of  stannous  chloride  to  the  hot 
ferric  chloride  solution  until  the  iron  is  decolorized,  and  allowing 
the  covered  beaker  to  heat  until  the  liquid  boils.  Allow  to  settle 
overnight,  if  possible. 

Prepare  an  asbestos  felt  by  extracting  with  hydrochloric  acid, 
igniting  it,  and  then  taking  the  "ignited"  weight.  Moisten  the 
felt,  dry  in  the  oven,  cool,  and  take  a  " dried"  weight.  After 
weighing  the  washed  and  dried  precipitates  of  selenium  or  tel- 
lurium, or  both,  deduct  the  tare  weight  obtained  by  drying. 
Finally  ignite  the  felt  as  a  check. 

A  felt  will  occasionally  suffer  a  slight  loss  in  washing,  in  spite 
of  the  usual  care.  Selenium  and  tellurium  are  separated,  if 
desired,  by  fractional  precipitation  with  sulphur  dioxide  as 
in  (a).  Refer  to  the  shorter  combination  method  of  the  author, 
in  connection  with  the  arsenic  and  antimony  determination  (7, 
Chapter  XII). 

Zinc.  —  The  separation  of  zinc  is  included  and  described 
with  the  method  for  cobalt  (6)  and  nickel  (7). 


PART  IV 

CHAPTER  XIV 
ANALYSIS  OF  THE  PRINCIPAL  COMMERCIAL  ALLOYS  OF  COPPER 

Introduction.  —  This  chapter  presents  the  standard  technical 
methods  of  one  of  the  largest  American  brass  companies.  A 
description  forwarded  by  Dr.  Toisten  of  the  Mansfeld  Brass 
Works  shows  that  the  European  methods  for  straight  brass  or 
bronze  are  practically  identical  with  those  to  be  described. 
Tests  for  nickel  and  spelter  are  also  included,  the  latter  being 
the  one  proposed  as  a  standard  by  the  Committee  on  non-ferrous 
alloys  of  the  American  Chemical  Society.  The  analysis  of 
antifriction  metals  and  other  special  complex  alloys  is  well 
described  in  another  recent  work.1 

COPPER  IN  ORDINARY  BRASS 

1.  In  the  Absence  of  Tin.  —  One  gram  of  drillings  are 
weighed  into  a  tall  200  c.c.  beaker  and  dissolved  in  a  mixture 
of  5  c.c.  of  sulphuric  acid  (d.,  1.84),  2  c.c.  of  nitric  acid  (d.,  1.42), 
and  18  c.c.  of  water.  (As  in  previous  chapters,  all  acids  are 
understood  to  be  of  full  strength  and  of  the  best  grade,  unless 
otherwise  specified.)  Dissolve  the  sample  by  heating,  dilute  the 
solution  to  about  120  c.c.,  and  introduce  a  split  platinum  cylinder, 
having  a  total  surface  of  100  sq.  cm.  Electrolyze  overnight  with  a 
current  density  of  .5  ampere.  The  process  may  be  hastened  by 
the  use  of  rotating  electrodes  and  gauze  cathodes,  or  preferably 
by  the  use  of  the  Frary  selenoid2  described  in  Chapter  I. 

If  the  assays  are  finished  by  the  slow  process,  wash  off  the 
electrodes  and  split  watch-glass  covers  at  the  beginning  of  work 
the  next  day,  and  continue  the  current  for  about  one  hour 
longer.  Test  the  electrolyte  for  the  end-point  by  transferring 
about  1  c.c.  of  the  liquid  to  a  porcelain  test  plate  and  adding  a 
few  drops  of  fresh  hydrogen  sulphide  water.  Continue  the  elec- 

1  Price  &  Meade,  The  Technical  Analysis  of  Brass. 

2  J.  Am.  Chem.  Soc.  29,  1592. 


THE  PRINCIPAL  COMMERCIAL  ALLOYS  OF  COPPER    237 

trolysis  until  there  is  no  visible  discoloration  in  the  test.  The 
cathode  is  removed  quickly,  plunged  into  a  large  beaker  of 
water,  dipped  twice  into  alconol,  the  excess  shaken  off,  and  the 
remainder  burned,  moving  the  cathode  continually. 

(Colorless  denatured  "pyro"  alcohol  of  about  94  per  cent 
strength  is  as  safe  to  use  as  the  best  grade,  at  a  fraction  of 
the  expense.)  The  use  of  dilute  mixed  acid  avoids  the  necessity 
of  evaporating  to  fumes,  as  the  nitric  acid  remaining  in  solution 
secures  uniformly  good  results. 

LEADED  BRASS   CARRYING  TIN 

2.  Technical  Estimation  of  Tin.  —  (In  this  connection,  refer 
also  to  alloys  with  iron  and  phosphorus.)  To  1  gram  of  drill- 
ings or  clippings  add  10  c.c.  of  strong  nitric  acid.  When  the 
action  has  ceased,  bring  to  a  boil,  add  50  c.c.  of  boiling  water, 
and  let  stand  until  the  metastannic  acid  has  settled  (about  one 
hour),  keeping  the  temperature  just  below  the  boiling  point. 
It  is  important  to  keep  this  solution  hot  and  filter  hot,  for  if  the 
liquid  cools,  the  metastannic  acid  becomes  partly  soluble.  Filter 
off  the  tin  on  a  double  7  cm.  paper,  keeping  the  solution  hot. 
It  may  be  necessary  to  return  the  first  portion  of  solution  to  the 
filter  in  order  to  have  it  run  clear.  J.  T.  Baker's  ashless  filters 
hold  the  tin  better  than  any  other  tried.  Some  of  the  especially 
close  grades  of  washed  papers  hold  the  moist  metastannic  acid 
properly  but  work  so  slowly  that  nothing  is  gained  by  using 
them.  Wash  the  tin  residue  with  boiling  water  and  ignite,  while 
moist,  in  a  porcelain  or  platinum  crucible,  slowly  at  first  and 
finally  to  the  full  heat  of  a  Tirrell  burner.  The  tin  oxide  must 
be  ignited  to  a  constant  weight,  and  if  more  than  20  mg.  in 
weight,  the  blast  lamp  is  necessary  for  the  final  heating.  Weigh 
as  tin  dioxide,  SnC>2  factor,  .7881. 

Limitations.  —  The  metastannic  acid,  obtained  in  this  way, 
is  free  from  copper,  lead,  zinc,  and  nickel,  but  will  contain  iron 
if  it  is  present,  also  phosphorus.  Also,  the  preceding  method 
for  tin  is  inaccurate  in  the  analysis  of  an  alloy  containing  iron 
in  any  considerable  amount.  Metastannic  acid  precipitated  by 
nitric  acid  usually  carries  a  part  of  the  iron  present.  If  the 
quantity  of  iron  approximates  that  of  the  tin,  nitric  acid  will 
render  only  a  portion  of  the  tin  insoluble  even  with  evaporation 
to  hard  dryness,  but  it  is  very  unusual  to  find  such  conditions 


238  ANALYSIS  OF  COPPER 

in  wrought  brasses  and  bronzes.  Ordinarily,  iron  is  present  in 
such  small  amounts  as  to  be  negligible  in  its  effect.  If  much 
iron  or  phosphorus  is  present,  proceed  as  described  in  the 
methods  to  follow :  "  Alloys  containing  tin  with  iron,"  and 
" Alloys  containing  phosphorus." 

3.  Technical  Method  for  Lead.  —  To  the  filtrate  from  which 
the  metastannic  acid  has  been  removed,  or  to  the  nitric  acid 
solution  of  the  alloy  if  no  tin  is  present,  add  40  c.c.  of  "lead 
acid/'  the  preparation  of  which  is  given  in  the  following  para- 
graph. Evaporate  to  fumes  and  allow  to  cool.  Take  up  with  35 
c.c.  of  water,  heat  to  boiling,  then  allow  to  cool  and  settle  for 
five  hours  —  better  overnight.  Filter  off  the  lead  sulphate  on  a 
Gooch  crucible,  wash  with  "lead  acid,"  and  remove  the  filtrate. 
Wash  out  the  "lead  acid"  with  a  solution  of  equal  parts  of  water 
and  alcohol,  finally  with  alcohol  alone.  Ignite  and  weigh  the 
lead  sulphate  with  the  precautions  noted  in  Fresenius's  "Quanti- 
tative Analysis."  (The  factor  for  lead  is  .6831.) 

Composition  of  Lead  Acid.  —  This  is  a  solution  of  one 
volume  of  sulphuric  acid  (d.,  1.84)  in  seven  volumes  of  water, 
saturated  with  lead  sulphate.  The  solution  is  prepared  as 
follows :  300  c.c.  of  sulphuric  acid  are  poured  into  1800  c.c.  of 
water;  1  gram  of  lead  acetate  is  dissolved  in  300  c.c.  of  water 
and  added  to  the  hot  liquid  with  stirring.  The  solution  is 
allowed  to  settle  for  three  or  four  days  and  pouted  off  through 
a  thick  asbestos  filter  for  use. 

In  dealing  with  small  amounts  of  lead,  it  has  been  found 
in  the  precipitation  of  lead  in  (1  : 20)  sulphuric  acid  (the  best 
dilution)  that  the  volume  of  solution  is  often  so  large  in  propor- 
tion to  the  lead  present  that  a  serious  loss  results.  When  lead 
acid  is  used,  it  is  unnecessary  to  consider  the  solubility  of 
the  lead  sulphate  (that  is,  in  technical  foundry  work),  since 
the  solution  is  always  brought  back  to  the  same  volume  as  the 
volume  of  lead  acid  originally  added.  Consequently,  when  the 
lead  sulphate  is  filtered,  no  more  lead  remains  in  the  filtrate 
than  was  originally  added  in  the  dilute  sulphuric  acid. 

NOTE.  —  In  a  mutual  investigation  of  a  sample  of  complex 
"rolling-mill  brass"  for  the  U.  S.  Bureau  of  Standards,  it  has 
recently  been  determined  that  in  an  exact  analysis  of  such 
material,  the  electrolytic  deposition  of  lead  from  nitric  acid 


THE  PRINCIPAL  COMMERCIAL  ALLOYS  OF  COPPER    239 

solution  as  the  peroxide  is  111019  accurate  than  precipitation  as 
sulphate.  Copper  and  zinc  salts  have  a  slight  solvent  action  on 
sulphate  of  lead,  so  that  the  assumption  on  which  leaded  acid 
is  prepared  and  used  is  not  strictly  true,  if  the  solution  contains 
much  copper  and  zinc.  After  the  lead  peroxide  has  been  cor- 
rected for  a  trace  of  tin  oxide  and  iron  oxide  which  it  may 
contain,  the  result  is  still  a  little  higher  by  electrolysis. 

4.  Lead  by  Electrolysis.  —  Lead  in  leaded  brass  may  also  be 
determined  by  dissolving  1  gram  in  10  c.c.  of  nitric  acid  and 
proceeding  according  to  the  exact  electrolytic  method  8,  described 
under  the  title  "  Impurities  in  Brass."     One  gram  is  the  quan- 
tity used  in  works  tests  for  the  rapid  determination  of  foundry 
mixtures. 

5.  Copper  in  Leaded  Brass. — To  the  filtrate  from  the  lead 
sulphate  in  3,  add  3  c.c.  of  (1  :  1)  nitric  acid,  bring  to  the  proper 
volume,  and  electrolyze  as  in  the  first  method  for  copper  (1). 

6.  Zinc  in  Leaded  Brass.  —  This  element  is  usually  taken  by 
difference  but  may  be  precipitated  as  phosphate.     The  electro- 
lyte from  5  may  also  be  titrated  as  described  in  the  "  Analysis 
of  German  silver"  (23). 

EXACT  DETERMINATION   OF  IMPURITIES  IN  BRASS 

7.  Lead  as  Sulphate,  — in  Absence  of  Tin. — When  the  amount 
of  lead  is  small  (less  than  .5  per  cent),  a  5-gram  sample  is  dis- 
solved in  25  c.c.  of  nitric  acid,  120  c.c.  of  lead  acid  is  added,  and 
the  liquid,  if  tin  is  absent,  evaporated  to  fumes.    Take  up  with 
105  c.c.  of  water,  boil,  settle,  and  filter  as  described  under  "  leaded 
brass."     If  tin  is  present,  as  is  shown  by  a  milkiness  in  the 
nitric  acid  solution  after  expulsion  of  nitrous  fumes,  add  125  c.c. 
of  boiling  water,  allow  the  metastannic  acid  to  settle,  and  filter 
off  exactly  as  for  the  1-gram  sample.    Add  120  c.c.  of  lead  acid 
to  the  filtrate  and  proceed  as  above  directed. 

8.  Exact  Electrolytic  Method  for  Lead.  —  For  small  amounts 
of  lead  the  previous  method  has  been  largely  superseded  by  "the 
electrolytic,  which  is  more  exact  (as  noted  in  3),  if  corrections 
are  made  for  traces  of  oxides  of  tin  and  iron  contained  in  the 
anode  deposit,  when  these  elements  are  in  solution  with  the  lead 
and  copper.     If  manganese  is  present  in  the  alloy,  it  will  also 
partially  deposit  with  the  lead. 


240  ANALYSIS  OF  COPPER 

Weigh  a  5-gram  sample  into  a  250  c.c.  wide  beaker.  Dissolve 
in  25  c.c.  of  nitric  acid  and  dilute  to  150  c.c.  with  water.  Elec- 
trolyze  with  current  reversed,  i.e.,  with  the  sheet  electrode  for 
the  anode, — first,  for  one-half  hour  at  .1  ampere  per  solution 
and  then  three  hours  at  .5  ampere.  Test  by.  exposing  a  clean 
surface  to  the  liquid.  When  this  test  shows  the  deposition  to 
be  complete,  remove  the  electrode,  wash  with  water,  and  then 
with  alcohol.  Dry  in  an  oven  at  least  half  an  hour,  and  finally 
cool  and  weigh  as  lead  dioxide.  For  lead  the  factor  .8643  is 
used,  following  the  results  of  Dr.  E.  F.  Smith  and  others.  If 
the  lead  is  excessive,  it  is  best  to  employ  a  gauze  electrode  to 
prevent  flaking  of  the  deposit. 

In  Presence  of  Tin.  —  Dissolve  5  grams  in  25  c.c.  of  nitric 
acid,  dilute  with  125  c.c.  of  boiling  water,  and  filter  off  the 
metastannic  acid  exactly  as  in  2.  In  very  exact  work,  dissolve 
the  tin  compound  in  hot  ammonium  sulphide  containing  am- 
monium chloride,  filter,  dissolve  the  washed  black  sulphides  from 
the  paper,  and  return  them  to  the  copper  solution.  In  the  solu- 
tion determine  the  lead  as  already  directed.  The  deposit  may 
be  removed  after  weighing  by  the  solvents  described  under 
" Electrolysis  of  Lead  in  Copper"  (page  222).  To  obtain 
the  correct  weight  of  the  platinum,  it  should  be  ignited  and 
weighed  again  after  cleaning,  as  it  loses  weight  perceptibly 
during  electrolysis. 

9.  Iron,  Exact  Method. — Dissolve  5  grams  of  brass  in  25  c.c. 
of  nitric  acid,  boil  off  nitrous  fumes,  dilute,  and  add  ammo- 
nium chloride  and  ammonia  in  excess.  Boil,  filter  on  an  S.  &  S. 
black  ribbon  paper,  wash  with  dilute  ammonia  and  then  with 
hot  water.  Dissolve  the  iron  precipitate  in  hot  (1:1)  hydro- 
chloric acid  and  reprecipitate  with  ammonia.  Dissolve  the 
ferric  hydroxide  after  the  second  precipitation  in  hot  (1  : 4)  sul- 
phuric acid  on  the  filter,  washing  out  thoroughly  with  dilute  acid 
and  hot  water.  Add  40  c.c.  of  (1  : 1)  sulphuric  acid,  pass  through 
a  Jones'  reductor  (or  add  hydrochloric  acid  and  decolorize  with 
one  drop  of  stannous  chloride  in  excess).  Then  titrate  with 
potassium  permanganate.  For  the  use  of  the  reductor,  consult 
"The  Chemical  Analysis  of  Iron"  by  Blair.  If  the  reduction  is 
made  by  stannous  chloride,  add  5  c.c.  of  a  saturated  solution  of 
mercuric  chloride  and  10  c.c.  of  titrating  solution  to  secure  a 
good  end-point.  (See  7,  Chapter  V.)  For  brass,  German  silver, 


THE  PRINCIPAL  COMMERCIAL  ALLOYS  OF  COPPER    241 

and  spelter  make  the  permanganate  solution  with  .3  gram  of 
the  crystals  per  liter,  and  standardize  against  .015  to  .018  gram 
of  pure  iron  wire.  One  c.c.  (ft  solution  then  equals  about  .0005 
gram  of  iron. 

In  Presence  of  Traces  of  Tin.  —  In  such  a  case,  the  insoluble 
metastannic  acid  must  be  removed  as  in  8,  and  the  filter  and 
contents  extracted  with  about  30  c.c.  of  warm  yellow  ammonium 
sulphide,  containing  1  gram  of  ammonium  chloride.  The  iron 
sulphide,  thus  obtained,  is  dissolved  in  dilute  nitric  acid  and 
returned  to  the  original  solution  of  the  alloy. 

ALLOYS   CONTAINING   TIN   WITH  IRON 
(Examples:  Manganese  Bronze,  Phospho-Bronze) 

10.  Copper   Assay,   for   Control   of   Mixtures.  —  Dissolve   a 
1-gram  sample  in  10  c.c.  of  nitric  acid,  boil,  wash  down,  and 
bake  thoroughly.     Moisten  with  nitric  acid,  dilute,  boil,  allow 
to  settle,  and  filter  off  all  possible  tin  oxides,  exactly  as  for  brass 
(2).     The  filtrate  contains  some  of  the  tin,  notwithstanding  the 
baking.     Add  to  the  filtrate  10  c.c.  of  (1  :  1)  sulphuric  acid  and 
evaporate  to  strong  fumes.     Dilute  to  about  120  c.c.  and  elec- 
trolyze  as  usual  for  copper.     When  the  deposition  is  complete, 
the  solution  may  show  a  yellow  color  on  the  spot  plate  with 
hydrogen  sulphide  water,  due  to  the  tin  present  in  solution,  but 
there  should  be  no  darkening  of  the  cathode  copper.    If  darken- 
ing occurs,  the  cathode  deposit  may  be  dissolved  in  nitric  acid 
and  the  tin  removed  easily   (since  iron  is  no  longer  present). 
The   copper  may  then  be  reprecipitated.     This  purification  is 
seldom  necessary  in  routine  work. 

11.  Exact  Electrolysis  for  Copper.  —  The  next   modification 
was   developed  by  the   author  in  analyzing  the  "  Rolling  Mill 
Brass"  for  the  U.  S.  Bureau  of  Standards.    Dissolve  5  grams 
of  drillings  in  25  c.c.  of  nitric  acid  and  75  to  125  c.c.  of  water, 
then  filter  off  and  purify  the  metastannic  acid  with  warm  yellow 
ammonium  sulphide  exactly  as  in  8.    Dissolve  the  trace  of  copper 
sulphide,  etc.,  in  5  c.c.  of  nitric  acid,  diluted  with  2  parts  of 
water,  and  return  it  to  the  main  solution  which  has  been  already 
treated  with  10  c.c.  of  sulphuric  acid  and  evaporated  to  fumes. 
The   diluted   solution,    which   contains   traces   of   dissolved   tin, 
should  then  be  filtered  from  the  lead  sulphate. 

Five  cubic  centimeters  of  nitric  acid  should  be  present  in  the 


242  ANALYSIS  OF  COPPER 

solution.  It  is  possible  to  deposit  the  copper  and  lead  simultane- 
ously from  a  pure  nitric  acid  solution,  if  preferred,  the  one  on 
the  cathode,  and  the  other  on  the  anode,  which  should  also  be  a 
cylinder,  or  dish. 

The  trace  of  tin  in  the  first  deposit  of  copper  is  easily  re- 
moved by  standing  the  cathode  in  a  tall  beaker  and  adding  40  c.c. 
of  the  "acid  mixture"  used  for  the  electrolytic  assay  of  re- 
fined copper  (2,  Chapter  XI).  Dilute  with  sufficient  water  to 
cover  the  plate,  cover  the  beaker  with  a  glass  perforated  with 
a  small  hole  for  the  stem  of  the  electrode,  and  allow  to  stand  on 
the  steam  plate  until  dissolved.  Repeat  the  electrolysis.  As  the 
second  electrolyte  is  free  from  iron,  the  last  deposit  will  be  free 
from  tin,  and  the  second  electrolyte  may  be  subsequently  com- 
bined with  the  first  to  obtain  a  complete  recovery  of  the  tin. 

Rapid  Assay.  —  Use  a  rotating  anode,  or  better,  the  Frary 
solenoid,  observing  the  precautions  indicated  in  the  rapid  assay 
of  refined  copper  (Chapter  XI)  : — Current  requirement,  4  to  4.5 
amperes  per  square  decimeter  of  immersed  cathode  surface. 

12.  Tin  and  Iron  in  Bronze  (Special  Method) .  —  This  modi- 
fication was  reported  by  Bassett  and  Merrill  in  the  assay  of  U.  S. 
standard  "  Rolling  Mill  Brass."     Five-gram  samples  should  be 
treated,  if-  results  are  to  be  reported  to  .01  per  cent.    Otherwise, 
dissolve  a  separate  1-gram  sample  in  10  c.c.  of  hydrochloric  and 
5  c.c.  of  nitric  acid.     Dilute,  and  make  a  double  precipitation 
with  ammonia  to  separate  tin  and  iron  from  the  copper.     Dis- 
solve the  oxides  the  first  time  in  hot  (1:1)  hydrochloric  acid 
and  the  next  time  in  very  hot  (1  : 2)  sulphuric  acid.    Wash  very 
thoroughly  with  this  acid.     Dilute,  filter  off  any  trace  of  lead 
sulphate,    and    saturate    the    solution    with    hydrogen    sulphide. 
Filter  off  the  tin  sulphide,  wash,  and  ignite  to  stannic  oxide, 
Sn(>2,  as  described  under  "phospho-bronze."     Heat  the  filtrate 
from  the  tin  sulphide  to  expel  the  hydrogen  sulphide,  oxidize 
with  nitric  acid,  and  add  ammonium  chloride  and  ammonia  in 
excess.     Boil,  filter,  wash  the  ferric  hydroxide,  dissolve  in  dilute 
sulphuric  acid,  and  titrate  as  in  method  9  for  iron  in  brass.    T.  J. 
Demorest  has  recently  devised  a  new  scheme  for  complex  alloys 
which  deserves  a  trial  (see  reference1)- 

13.  Tin  in  Phospho-Bronze.  —  In  alloys  of  this  kind,  copper, 
zinc,  and  tin  are  determined  in  one  sample.     The  metastannic 

1  J.  Ind.  and  Eng.  Chem.  6,  842. 


THE  PRINCIPAL  COMMERCIAL  ALLOYS  OF  COPPER    243 

acid  (containing  phosphorus)  js?  filtered  off  exactly  as  in  the 
analysis  of  brass  (2),  and  the  jcopper  and  zinc  estimated  as 
described. 

The  paper  with  the  tin  precipitate  is  extracted  in  a  small 
beaker  with  ammonium  polysulphide  and  ammonium  chloride, 
then  filtered  and  the  residue  washed  thoroughly  with  dilute 
yellow  ammonium  sulphide.  The  lead  and  iron  sulphides  are 
filtered  from  the  dissolved  tin,  and  the  polysulphide  solution 
is  made  acid  with  acetic  acid  (instead  of  sulphuric),  heated  to 
boiling,  and  filtered.  The  precipitated  tin  sulphide  is  ignited 
directly  with  the  moist  paper  to  stannic  oxide,  SnO2,  taking  care 
to  ignite  to  constant  weight.  This  ignition  must  proceed  slowly 
and  carefully  until  the  sulphur  is  roasted  off.  The  sulphur 
should  not  be  allowed  to  burn,  for  some  tin  sulphide  might  be 
volatilized.  The  ignition  is  best  started  in  a  porcelain  crucible, 
placed  upright  in  a  hole  in  a  piece  of  asbestos  board  in  which  it 
fits  tightly  near  the  top.  When  the  sulphur  is  expelled,  the  cru- 
cible is  ignited  in  a  slanting  position  upon  a  triangle.  If  the 
tin  oxide  weighs  over  20  mg.,  finish  with  the  blast  lamp. 

Impure  metastannic  acid  may  also  be  purified  by  igniting, 
mixing  with  three  parts  of  sodium  carbonate  and  three  parts 
sulphur,  and  fusing  in  a  porcelain  crucible.  Some  chemists  prefer 
to  place  the  small  crucible  inside  a  larger  one.1  The  fusion  is 
taken  up  with  hot  water,  boiled  to  insure  complete  precipitation 
of  foreign  sulphides,  filtered,  and  the  tin  finally  separated  with 
acetic  acid  as  above  described. 

PHOSPHORUS 

14.  By  Titration.  —  Dissolve  a  separate  1-gram  sample  in  a 
casserole  by  an  acid  mixture  containing  two  parts  of  hydro- 
chloric acid  and  one  of  nitric  acid.  Evaporate  to  dryness. 
Moisten  with  hydrochloric  acid,  evaporate  to  dryness  again, 
and  heat  to  dull  redness.  (This  removes  most  of  any  arsenic 
present.)  Moisten  with  hydrochloric  acid,  add  water  and  about 
3  c.c.  of  strong  ferric  chloride  solution,  make  alkaline  with  am- 
monia, boil  and  filter,  wash  with  dilute  ammonia,  and  then  with 
hot  water.  Dissolve  the  iron  precipitate  (which  carries  the 
phosphorus)  in  hot  (1  :  1)  hydrochloric  acid,  dilute,  and  satu- 

1  Blair,  The  Chemical  Analysis  of  Iron,  7th  Edition,  p.  95;  Year  Book 
Amer.  Soc.  Testing  Materials  (1915). 


244  ANALYSIS  OF  COPPER 

rate  the  liquid  with  hydrogen  sulphide.  Filter  off  the  tin  and 
copper  sulphides,  oxidize  the  filtrate  with  nitric  acid,  and  repre- 
cipitate  with  ammonia.  Dissolve  the  ferric  hydroxide  with  hot 
(1:4)  sulphuric  acid  into  an  Erlenmeyer  flask.  Add  ammonia 
to  the  solution  in  the  flask  until  it  is  alkaline,  make  slightly  acid 
with  nitric  acid,  add  ammonium  molybdate  solution,  and  pro- 
ceed as  in  the  determination  of  "phosphorus  in  steel." 

The  contributing  chemists  employ  the  ferric-alum  modifica- 
tion of  the  permanganate  titration,  adopting  the  same  strength  of 
solution  as  for  iron  or  manganese,  —  3  grams  of  crystals  per 
liter.  The  " yellow  precipitate"  may  be  dissolved  in  ammonia, 
if  preferred,  the  solution  made  acid,  then  alkaline,  and  treated 
with  excess  of  magnesia  mixture. 

MANGANESE 

15.  Manganese  in  Alloys.  —  If  the  sample  contains  tin,  dis- 
solve 5  grams  in  25  c.c.  of  nitric  acid,  dilute  with  125  c.c.  of 
boiling  water,  and  filter  off  the  metastannic  acid  as  described 
under  " Brass"  (2  to  8).    If  tin  is  absent,  dissolve  as  before  with- 
out filtration.     In  either  case,  evaporate  the  solution  to  a  sirup 
in  a  tall  500  c.c.  beaker,  add  100  c.c.  of  nitric  acid  and  5  grams 
of  potassium  chlorate,  and  proceed  as  in  William's  modification 
of  Ford's  method.1 

In  this  process,  the  first  precipitate  of  manganese  dioxide 
may  contain  a  little  impurity,  which  would  require  re-solution 
and  reprecipitation  with  nitric  acid  and  potassium  chlorate. 
The  ferrous  ammonium  sulphate  solution  should  be  composed 
of  100  grams  of  the  crystals,  50  c.c.  of  sulphuric  acid  (d.,  1.84), 
and  2000  c.c.  of  water.  Usually,  10  c.c.  of  solution  are  sufficient 
to  dissolve  the  precipitated  manganese  dioxide.  The  potassium 
permanganate  contains  3  grams  of  the  crystals  per  liter,  or  ten 
times  the  strength  used  for  iron  in  brass  (9).  It  is  standardized 
against  .10  to  .12  gram  of  pure  iron  wire.  To  estimate  the 
manganese,  dissolve  the  dioxide  in  10  c.c.  of  the  ferrous  sulphate 
solution,  protecting  it  from  the  air.  Immediately  titrate  back  the 
unused  ferrous  salt  with  the  permanganate.  Fe  X  .4919  =  Mn. 

16.  Gravimetric  Method.  —  Manganese  may  also  be  deter- 
mined by  Ford's  method,1  dissolving  the  sample  and  oxidizing 
the  manganese  as  in  the  previous  method.     The  first  precipitate 

1  Blair,  Chemical  Analysis  of  Iron,  7th  Edition,  114-118. 


THE  PRINCIPAL  COMMERCIAL  ALLOYS  OF  COPPER    245 

should  be  dissolved  and  reprecipitated  for  purification.  After 
dissolving  the  purified  dioxide/  the  manganese  is  finally  thrown 
down  by  a  large  excess*  of  amrifonium  phosphate  in  a  boiling, 
slightly  ammoniacal  solution.  Add  the  precipitant  slowly  to  the 
hot  liquid,  stirring  rapidly.  Continue  heating  and  stirring  until 
the  crystals  assume  the  true  color  and  silky  appearance.  Filter, 
wash,  and  dry  the  precipitate;  then  ignite  carefully  to  avoid 
any  reduction.  Use  the  conversion  table  of  Chapter  XVI. 

The  sodium  bismuthate  method  is  also  very  exact.  (See 
method  25,  Chapter  VI.) 

ALLOYS   CONTAINING  A  LITTLE   NICKEL 

17.  Nickel.  —  In  alloys  where  there  is  a  relatively  low  ratio 
of  nickel  to  zinc  (not  over  1  to  15),  a  method  is  desirable  which 
will  permit  a  quick  and  accurate  separation  of  the  small  amount 
of  nickel  from  the  large  amount  of  zinc,  with  the  final  deter- 
mination of  the  nickel  by  electrolysis. 

In  the  complete  analysis  of  any  complex  alloy,  the  filtrate 
from  tin  and  iron  is  taken  for  the  separation  of  nickel  and  zinc. 
Precipitate  the  nickel  by  dimethyl  glyoxime  from  the  hot,  slightly 
ammoniacal  filtrate  according  to  the  special  method  below,  and 
follow  with  the  estimation  of  the  zinc  in  the  filtrate  from  the 
nickel.  The  sodium  potassium  tartrate  is  omitted,  as  no  iron 
is  present. 

18.  Special  Method  for  Nickel.  —  Dissolve  a  special  1-gram 
sample  exactly  as  in  the  determination  of  copper  in  brass  (1,  5), 
and  remove  the  copper  by  electrolysis.     A  little  copper  in  the 
electrolyte  does  no  harm.     Concentrate  the  solution  to  about 
100  c.c.,  add  1  gram  of  ammonium  chloride,  then  10  c.c.  of  a  20 
per  cent  solution  of  sodium  potassium  tartrate.     Neutralize  with 
ammonia,  adding  about  2  c.c.  in  excess,  and  then  stir  in  5  c.c. 
of  a  1  per  cent  alcoholic  solution  of  dimethyl  glyoxime  for  each 
per  cent  of  nickel.    This  method  is  due  to  O.  Brunck  and  Tschu- 
gaeff.1    Allow  the  solution  to  stand  for  one-half  hour,  filter,  and 
wash  with  very  dilute  ammonia.     Dissolve  the  red  precipitate 
in  hot  (1  :  1)  hydrochloric  acid,  add  10  c.c.  of  (1  :  1)  sulphuric 
acid,  and  evaporate  to  strong  fumes  of  sulphur  trioxide.    Dilute, 
neutralize  with  ammonia,  and  add  20  c.c.  in  excess;   electrolyze 

1  Zeit.  Angew.  Chem.  20,  834  and  3844. 


246  ANALYSIS  OF  COPPER 

with  a  current  of  .3  ampere  per  solution.  Test  for  the  end-point 
with  fresh  hydrogen  sulphide  water,  as  in  the  "  determination  of 
copper  in  brass"  (1  and  5). 

NOTE.  —  The  Frary  solenoid  may  be  used  to  advantage  with 
a  current  of  4  amperes  per  solution.  With  this  rapid  circulation 
and  heavy  current  the  time  is  reduced  to  one  hour. 

SULPHUR  IN  BRASS   OR  NICKEL  ALLOYS 

19.  Precipitation  as  Barium  Sulphate.  —  Weigh  duplicate  10- 
gram  samples  of  drillings  into  a  600  c.c.  tall-lipped  beaker.  Add 
about  .5  gram  of  pure  sodium  carbonate.  Cover  and  then  add 
50  c.c.  of  nitric  acid.  When  the  action  has  ceased,  boil  off  red 
fumes,  evaporate  off  the  bulk  of  the  solution,  and  allow  to  bake 
overnight  at  tlje  temperature  of  the  steam  bath.  Fill  to  the 
lip  with  warm  water.  There  should  be  present  a  layer  about 
i  inch  (6  mm.)  thick,  composed  of  basic  salts  of  copper.  Add 
3  c.c.  of  (1  :  1)  nitric  acid  and  electrolyze,  placing  the  beaker  in 
a  large  Frary  solenoid,  or  rotary  device.  The  lead  may  be 
removed  at  the  anode  as  copper  is  taken  out  at  the  cathode. 
When  the  copper  is  gone,  evaporate  to  small  volume,  cover  the 
beaker,  add  75  c.c.  of  hydrochloric  acid,  and  boil  down  to  a 
small  volume.  Add  75  c.c.  more  hydrochloric  acid  and  evap- 
orate to  dryness.  Take  up  with  water,  make  alkaline  with 
ammonia,  and  dilute  to  the  lip  of  the  beaker. 

Then  proceed  to  remove  the  nickel  and  zinc  by  electrolysis, 
using  a  large  iron  cathode  and  the  Frary  rotary  device.  When 
the  solution  is  colorless,  wash  down  the  electrodes;  remove 
them,  and  heat  the  solution  to  boiling.  Let  settle  and  filter 
through  an  11  cm.,  black  ribbon  paper  into  a  600  c.c.  tall  beaker. 
Make  the  solution  acid  with  hydrochloric  acid  and  evaporate 
until  the  ammonium  chloride  starts  to  crystallize.  Cover  and 
add  50  c.c.  of  nitric  acid.  Boil  down  to  small  bulk;  add  25  c.c. 
of  hydrochloric  acid  and  boil  until  no  more  chlorine  is  evolved. 
Wash  down  the  cover  and  evaporate  to  dryness  to  dehydrate 
any  silica  present.  Moisten  with  hydrochloric  acid  and  take 
up  with  20  c.c.  of  hot  water.  Filter  into  a  small  beaker.  Heat 
the  filtrate  to  boiling,  add  5  c.c.  of  5  per  cent  barium  chloride 
solution,  drop  by  drop,  with  stirring.  Allow  to  settle  at  least 
five  hours,  filter  on*  a  small  ashless  paper,  and  wash  with  hot 


THE  PRINCIPAL  COMMERCIAL  ALLOYS  OF  COPPER    247 

water.  Ignite  cautiously  in  .%a  small  porcelain,  or  platinum, 
crucible,  and  then  heat  to  bright  redness  for  twenty  minutes. 
Cool  and  weigh  the-  barium  sulphate.  BaSC>4  X  .1374  =  sul- 
phur (S). 

NOTE.  —  The  utmost  precautions  should  be  taken  to  prevent 
contamination  with  sulphur  in  any  form.  Avoid  gas-heating, 
except  by  gasolene  gas.  Run  a  blank  analysis;  that  is,  take  a 
600  c.c.  beaker,  add  to  it  all  the  reagents,  and  subject  the  con- 
tents to  the  same  operations  as  the  samples  of  drillings,  and  at 
the  same  time.  Deduct  any  barium  sulphate  obtained  from  the 
result  of  the  actual  assay.  If  this  blank  amounts  to  .0020  gram, 
it  is  a  sign  of  poor  work  and  the  analysis  should  be  repeated. 
Wash  out  all  beakers,  funnels,  etc.,  with  distilled  water  before 
use. 

ZINC  IN  BRASS  AND  BRONZE 

20.  Volumetric  Method.  —  The   filtrate   from   the   iron   pre- 
cipitation, or  from  the  nickel  separation  when  that  element  is 
present,  is  taken  for  the  determination  of  zinc.    In  brass  works, 
the  custom  is  to  employ  rapid  titration.     Add  20  c.c.  of  nitric 
acid  (d.,  1.42)  to  the  filtrate  from  the  nickel  precipitation.    Boil, 
add  some  ferric  chloride,  citric  acid,  and  ammonia;  then  titrate 
with  potassium  ferrocyanide  exactly  as  directed  in  the  analysis  of 
nickel  alloys  (23). 

21.  Gravimetric   Method.  —  For   an   occasional   analysis,   or 
in  umpire  work,  some  chemists  prefer  a  precipitation  and  igni- 
tion of  zinc  phosphate.     The  filtrate  from  the  nickel  separation 
(16)  may  be  used  after  boiling  out  the  alcohol,  or  a  new  sample 
may  be  treated  as  follows :   Precipitate  lead  and  copper  from  the 
acid  solution  of  the  sample  on  sheet  aluminum  according  to  (25) 
Chapter  VI.     To  the  final  solution  (volume  about  50  c.c.)  add 
50  c.c.  of  a  10  per  cent  solution  of  ammonium  phosphate,  make 
just  alkaline  to  litmus,  then  acid  with  1  c.c.  of  acetic  acid  in 
excess.    Heat  just  below  boiling  for  about  an  hour.    This  treat- 
ment should  cause  the  zinc  to  become  granular.    Allow  to  settle, 
filter,  wash  with  hot  water,  and  dry  the  substance.     Char  the 
filter  separately,  ignite  the  phosphate  with  care,  cool  the  crucible, 
and  weigh  the  precipitate.     (To  obtain  the  weight  of  the  zinc, 
multiply  the  weight  of  the  ignited  pyrophosphate,  Zn2P2O7  — , 
by  .4289. 


248  ANALYSIS  OF  COPPER 

ANALYSIS   OF  NICKEL  ALLOYS 
(Example,  German  Silver,  Monel  Metal.) 

22.  Copper.  —  The   copper  is   determined   as   in   brass.     In 
arranging  the  cathode,  allow  it  to  project  about  J  inch  above  the 
solution.     When  the  copper  is  apparently  all  precipitated,  wash 
down  the  cover  glasses  and  sides  of  the  beaker,  which  will  cause 
the  solution  to  cover  the  cathode.    If  no  sign  of  copper  is  seen  on 
the  clean  platinum,  it  indicates  that  the  deposition  is  complete. 
If  copper  does  appear,  the  electrolysis  must  be  continued  several 
hours,  or  until  the  solution  polarizes  and  gas  bubbles  come  off 
freely  from  the  cathode. 

23.  Zinc.  —  After  removing   the   copper   as   above,    concen- 
trate the  solution  to  about  75  c.c.  and  transfer  to  a  tall  500  c.c. 
beaker,  make  just  alkaline  with  ammonia,  then  acid  by  adding 
2  c.c.   of  formic  acid   (d.,  1.2),  then  add  enough  ammonia  to 
barely  restore  the  blue  color.     Finally,  add  formic  acid  of  the 
same  density  in  the  proportion  of  38  c.c.  for  every  200  c.c.  of 
final  volume  of  solution.    Heat  to  boiling  and  pass  a  rapid  stream 
of  hydrogen  sulphide  gas  into  the  liquid  for  fifteen  minutes,  using 
a  fine  jet  tube.     Start  the  gas  before  putting  the  tube  into  the 
liquid,  for  if  the  interior  of  the  tube  becomes  wet  with  the  solu- 
tion, nickel  sulphide  will  deposit  on  the  inside  of  the  tube.    Filter 
off  the  pure  white  zinc  sulphide  and  wash  with  hot  water;    dis- 
solve in  hot  dilute  hydrochloric  acid;    filter  off  the  sulphur  and 
wash  the  paper.    Any  slight  black  residue  may  be  dissolved  in  a  few 
drops  of  nitric  acid  and  returned  to  the  nickel  solution.     The  nickel 
solution  should  then  be  heated  up  and  more  hydrogen  sulphide 
passed  to  make  sure  that  the  zinc  is  all  out.     To  the  hydro- 
chloric acid  solution  of  the  zinc  sulphide,  add  nitric  acid  and  boil 
to  oxidize  the  hydrogen  sulphide.    Cool  and  add  3  c.c.  of  a  strong 
solution  of  ferric  chloride,  20  c.c.  of  a  saturated  citric  acid  solu- 
tion, and  ammonia  to  make  distinctly  alkaline.     A  very  large 
excess  of  ammonia  should  be  avoided.    Heat  this  solution,  which 
should  have  a  volume  of  from  250  to  300  c.c.,  to  boiling,  and 
titrate  with  potassium  ferrocyanide  solution. 

Titration.  —  To  determine  the  end-point  with  ferrocyanide, 
the  pits  in  the  porcelain  test  plate  are  filled  with  a  50  per  cent 
acetic  acid  solution.  When  the  titration  is  nearly  completed 
(which  may  be  judged  from  the  conditions),  two  drops  are  taken 


THE  PRINCIPAL  COMMERCIAL  ALLOYS  OF  COPPER    249 

out  and  added  to  the  acetic  acid  in  one  of  the  pits.  This  gives 
a  slight  greenish  tint,  and  a  few  drops  more  of  the  ferrocyanide 
are  added  and  another  portion  taken  out.  This  is  continued 
until  the  end-point,  which  is  a  distinct  blue,  is  reached.  On 
making  acid  with  the  two  drops  of  acetic  acid,  a  Prussian  blue 
is  not  formed  until  all  the  zinc  has  been  precipitated  as  ferro- 
cyanide. It  requires  about  J  c.c.  of  the  ferrocyanide  to  give  a 
distinct  end-point  in  250  c.c.  of  solution  containing  no  zinc.  The 
ferric  chloride  is  added  as  an  indicator,  but  if  the  solution  con- 
tains sufficient  iron,  as  it  does  in  the  case  of  certain  zinc  ores, 
the  addition  of  this  iron  is  not  necessary.  Small  amounts  of 
aluminum,  lime,  and  magnesium  make  no  difference  in  this 
titration. 

The  correction  for  the  blank  in  getting  the  end-point  must 
be  made  by  the  operator.  This  titration  is  difficult  for  an  inex- 
perienced operator,  but  for  one  used  to  the  method  it  is  one  of 
the  most  accurate  methods  for  the  determination  of  zinc  and  is 
both  rapid  and  easy  to  handle.  It  is  accurate  within  about  .2 
per  cent  and  the  experienced  operator  can  check  his  own  results 
within  about  .1  per  cent.  This  titration  must  be  carried  out 
in  every  case  in  exactly  the  same  manner  as  the  standardiza- 
tion. 

The  potassium  ferrocyanide  solution  is  made  up  by  dissolving 
80  grams  of  the  salt  in  2500  c.c.  of  water  and  standardizing 
against  a  solution  of  pure  metallic  zinc.  The  potassium  ferro- 
cyanide should  be  allowed  to  stand  at  least  six  weeks  before  use; 
in  that  time  changes  which  occur  in  such  solutions  will  have 
completed  themselves,  and  the  standardization  value  will  remain 
permanent.  This  value  is  ascertained  by  weighing  out  2  grams 
of  zinc,  dissolving  the  metal  in  nitric  acid,  and  making  up  to 
1000  c.c.  Take  100  c.c.  of  the  solution,  add  5  c.c.  of  nitric  acid, 
3  c.c.  of  ferric  chloride,  and  20  c.c.  of  saturated  citric  acid 
solution,  dilute,  and  make  distinctly  alkaline  with  ammonia. 
The  final  volume  should  be  250  c.c.  Boil  and  titrate  while 
boiling  hot  with  the  ferrocyanide  solution  and  figure  the  zinc 
equivalent. 

24.  Alternative  Titration  for  Zinc.  —  This  alternative  method 
is  based  on  the  paper  entitled  "A  Proposed  Standard  Method," 
written  by  Frank  G.  Breyer.1 

1  8th  Int.  Cong,  of  Appl  Chem.  1, 162. 


250  ANALYSIS  OF  COPPER 

Proceed  as  in  23  until  the  pure  white  zinc  sulphide  has 
been  filtered  off  and  washed  with  hot  water.  Return  the  paper 
and  precipitate  to  the  original  500  c.c.  beaker  and  add  20  c.c.  of 
(1:1)  hydrochloric  acid.  When  the  zinc  sulphide  is  dissolved, 
filter  off  the  paper  together  with  some  sulphur  and  possibly  a 
little  nickel  sulphide,  which  may  be  treated  as  directed  in  23. 
Boil  the  solution,  containing  the  zinc,  slowly  for  about  fifteen 
minutes  to  expel  hydrogen  sulphide;  cool  and  wash  down.  Add 
13  c.c.  of  ammonia  (d.,  .90),  and  if  the  solution  is  not  then  alka- 
line, make  it  so  by  cautious  addition  of  ammonia.  There  must 
be  enough  hydrochloric  acid  present  to  neutralize  at  least  the 
above  amount  of  ammonia.  Make  the  solution  barely  acid 
again  with  hydrochloric  and  add  3  c.c.  of  concentrated  acid  in 
excess.  Add  1  c.c.  of  a  solution  of  ferrous  sulphate  containing 
3  grams  of  the  salt  per  liter,  dilute  nearly  to  200  c.c.,  heat  almost 
to  boiling,  and  titrate  with  potassium  ferrocyanide.  The  ferro- 
cyanide  employed  for  this  titration  contains  44  grams  of  the 
potassium  ferrocyanide  and  .3  gram  of  potassium  ferricyanide 
per  liter  and  is  prepared  at  least  six  weeks  before  use.  The 
end-point  is  a  sharp  change  in  the  color  of  the  solution  from  a 
turquoise  blue  to  a  "pea  green,"  and  with  several  more  drops 
to  a  "  creamy  yellow."  This  end-point  occurs  a  little  sooner 
than  the  one  with  uranium  nitrate,  and  is  easier  to  use,  as  the 
change  is  seen  directly  in  the  solution.  If  the  sample  does  not 
contain  at  least  3  per  cent  of  zinc,  which  can  be  estimated  by  the 
appearance  of  the  zinc  sulphide,  20  c.c.  of  a  standard  solution, 
containing  6  grams  of  pure  zinc  in  2000  c.c.,  are  added  from  a 
pipette  just  after  the  solution  to  be  titrated  has  been  boiled  to 
expel  the  hydrogen  sulphide,  and  the  solution  is  then  made 
ready  for  titration  as  described  above.  This  addition  of  zinc  is 
necessary  in  order  to  obtain  a  good  end-point. 

The  ferrocyanide  solution  is  standardized  in  the  following 
manner :  Six  grams  of  zinc  are  dissolved  in  40  c.c.  of  hydro- 
chloric acid  in  a  2-liter  flask,  the  solution  made  up  to  the  mark 
with  the  usual  precautions,  and  100  c.c.  taken  for  titration. 
Add  10  c.c.  of  hydrochloric  acid  (d.,  1.2)  and  13  c.c.  of  ammonia 
(d.,  .90)  If  the  solution  is  not  then  alkaline,  it  is  made  so 
with  further  addition  of  ammonia.  Acidify  again  with  hydro- 
chloric acid,  adding  the  acid  drop  by  drop,  and  an  excess  of 
3  c.c.  of  the  strong  acid.  After  addition  of  1  c.c.  of  the  ferrous 


THE  PRINCIPAL  COMMERCIAL  ALLOYS  OF  COPPER     251 

sulphate  solution  previously  >  described,  the  solution  is  diluted 
nearly  to  200  c.c.,  is  heated  almost  to  boiling,  and  is  treated  as 
described  above. 

NOTE,  on  Gravimetric  Method.  —  Any  laboratory  making  an 
occasional  analysis  only,  will  find  it  less  work  to  employ  a 
modification  of  the  Waring  method  described  under  "Zinc  in 
ores"  (17,  Chapter  VII),  and  in  the  "Analysis  of  Brass"  (21,  this 
chapter) . 

25.  Nickel  in  German  Silver.  —  Nickel  is  usually  taken  by 
difference  after  the  iron  has  been  determined.  If  the  estimation 
of  nickel  is  required,  after  filtering  out  the  sulphide  of  zinc, 
evaporate  the  nickel  solution  to  dryness,  then  cover  the  beaker, 
add  25  c.c.  each  of  hydrochloric  and  nitric  acids,  and  heat  to 
destroy  the  formates.  This  oxidation  with  aqua-regia  is  repeated 
until  all  the  formates  are  destroyed.  The  small  amount  of  nickel 
sulphide,  which  is  brought  down  by  the  zinc  sulphide  and  which 
is  filtered  off  from  the  hydrochloric  acid  solution  of  the  zinc 
sulphide,  must  also  be  added.  After  destroying  the  formates, 
add  3  c.c.  of  sulphuric  acid  and  evaporate  to  strong  fumes. 
Dilute,  neutralize  with  strong  ammonia,  and  add  20  c.c.  of 
strong  ammonia  in  excess,  making  about  125  c.c.  in  all.  Electro- 
lyze  with  a  current  of  .3  ampere  per  solution.  Test  the  solution 
for  the  end-point  by  fresh  hydrogen  sulphide  water  as  in  the  case 
of  copper. 

Rapid  Electrolysis. — The  author  has  found  the  Frary  solenoid 
to  be  well  adapted  to  the  deposition  of  nickel.  The  nickel 
ammonium  sulphate  is  a  better  conductor  of  the  current  than  a 
neutral  solution,  hence  the  liquid  should  contain  the  ammonium 
sulphate  and  be  kept  strongly  alkaline.  Current  4  amperes  per 
solution.  In  very  accurate  work,  the  deposit  should  be  dissolved 
in  nitric  acid,  the  cold  dilute  solution  treated  with  10  c.c.  of 
hydrogen  sulphide  water,  filtered,  and  the  residue  washed,  ig- 
nited, and  weighed.  If  no  copper  is  found,  the  residue  may  be 
assumed  to  be  platinum  carried  over  from  the  anode  by  the 
strong  current. 

26.  Iron  in  German  Silver.  —  Dissolve  2  grams  of  the  alloy 
in  15  c.c.  of  nitric  acid  and  proceed  exactly  as  in  the  determina- 
tion of  iron  in  brass. 

27.  Carbon  by  Combustion.  —  Place  5  grams  of  drillings  in  a 


252  ANALYSIS  OF  COPPER 

500  c.c.  beaker  and  add  300  c.c.  of  a  saturated  solution  of  copper- 
potassium  chloride  and  22.5  c.c.  of  hydrochloric  acid  (d.,  1.19). 
Stir  and  allow  to  stand  in  a  warm  place  overnight,  or,  if  neces- 
sary, hasten  the  operation  by  a  mechanical  stirrer.  Filter  on  a 
platinum  crucible  (made  up  with  ignited  asbestos),  wash  thor- 
oughly with  dilute,  hydrochloric  acid  and  fintilly  with  hot  water 
to  remove  all  chloride.  Place  the  Gooch  crucible  inside  a  Shinier 
crucible,  ignite  in  a  combustion  train,  and  determine  the  carbon 
in  exactly  the  same  way  as  "  carbon  in  steel."  It  is  absolutely 
essential  that  the  beakers  and  solutions  shall  be  protected  from 
dust  by  double  coverings  until  the  carbon  has  been  transferred 
to  the  combustion  apparatus. 

REFINED   NICKEL 

28.  Electrolytic  Assay.  —  Weigh  duplicate  2-gram  samples 
into  250  c.c.  beakers,  cover,  and  dissolve  in  30  c.c.  of  (1  :  1)  nitric 
acid.  Dilute,  add  about  5  grams  of  ammonium  chloride,  and 
make  alkaline  with  ammonia.  Heat  carefully  to  boiling  and 
filter  off  the  ferric  hydroxide  on  a  small  "black  ribbon"  S.  &  S. 
paper,  receiving  the  filtrate  in  a  tall  500'  c.c.  beaker.  Wash  with 
dilute  ammonia  and  with  hot  water.  Dissolve  the  precipitate  into 
the  original  250  c.c.  beaker  with  a  little  hot  (1:1)  hydrochloric 
acid.  Reprecipitate  with  ammonia,  filter,  and  combine  this 
filtrate  and  washings  with  those  from  the  first  precipitation. 
Stand  this  solution  on  a  hot  plate  to  concentrate  and  evaporate 
off  the  excess  of  ammonia.  Cover  and  add  50  c.c.  of  a  mixture 
of  equal  parts  of  nitric  and  hydrochloric  acids,  and  boil  to  small 
volume.  Cool,  add  20  c.c.  of  (1  :  1)  sulphuric  acid,  and  repeat 
the  treatment  with  nitric  and  hydrochloric  acids,  until  the 
ammonium  salts  are  entirely  expelled.  Wash  down,  remove 
cover  glass,  and  allow  the  solution  to  evaporate  to  strong  fumes. 
Dissolve  the  nickel  sulphate  in  water,  neutralize  with  ammonia 
(d.,  .90)  and  add  20  c.c.  in  excess.  Electrolyze  overnight  with  a 
current  of  .25  ampere  per  solution.  Test  with  hydrogen  sulphide 
as  in  preceding  methods.  The  cathode,  after  burning  off  the 
alcohol,  is  baked  in  the  oven  for  one  hour  at  about  105°  C.  The 
deposit  is  nickel  plus  cobalt  plus  copper.  No  attempt  is  ordi- 
narily made  to  determine  the  nickel  and  cobalt  separately. 
Copper  is  estimated  on  a  separate  sample,  and  the  amount  found  is 
subtracted  from  the  total  amount  of  the  copper  +  nickel  +  cobalt. 


THE  PRINCIPAL  COMMERCIAL  ALLOYS  OF  COPPER    253 

Iron,  if  present,  causes » slightly  high  results,  probably  being 
brought  over  mechanically  3$  hydroxide  and  weighed  as  oxide. 
Electrolyze  with  a  gauze  cathode  and  a  current  of  5  amperes  per 
solution  for  1J  hours  if  preferred,  using  some  rotary  device. 
This  deposit  may  be  purified  as  outlined  in  the  last  paragraph 
of  25. 

29.  Special  Assay  for  Copper.  —  Dissolve  a  5-gram  sample  in 
a  casserole,  using  50  c.c.  of  (1  :  1)   nitric  acid;    add  20  c.c.  of 
(1:1)  sulphuric  acid  and  evaporate  to  strong  fumes.     Add  about 
20  c.c.  of  water,  heat  until  nickel  sulphate  is  dissolved,  add  about 
10  grams  of  ammonium   chloride,  and  saturate  with  hydrogen 
sulphide  gas.     Filter  off  the  copper  sulphide  (which  may  contain 
a  little  nickel),  place  the  filter  and  contents  in  a  tall  200  c.c. 
beaker,  add  10  c.c.  of  (1  :  1)  sulphuric  and  25  c.c.  of  strong  nitric 
acid,  then  boil  down  to  strong  fumes.     If  the  filter  is  not  de- 
stroyed leaving  a  clear  solution,  more  nitric  acid  may  be  added, 
and  the  solution  boiled  down  to  fumes  again.     Dilute  to   120 
c.c.,  add  3  c.c.  of  (1  : 1)  nitric  acid,  and  electrolyze  as  usual  for 
copper. 

30.  Iron  in  Refined  Nickel.  —  Dissolve  a  2-gram  sample  in 
30  c.c.  of  (1  :  1)  nitric  acid,  dilute,  add  ammonium  chloride  and 
ammonia  in  excess,  and  proceed  exactly  as  in  "the  estimation  of 
iron  in  brass." 

STANDARD  ANALYSIS   OF  ZINC   SPELTER 

31.  Classification.  —  The    sub-committee    on    alloys    of    the 
American   Chemical   Society  recommends   a  method   of  testing 
spelter,   which   has  been   elaborated   from  those  originally  pro- 
posed by    Elliot    and    Storer l    and    Price,2    and   which    closely 
agrees  with  the  procedure  of  the  American  Society  for  Testing 
Materials.3     The  sampling  of  spelter  is  described  in  36,  Chapter 
II. 

Spelter  ordinarily  used  for  brass  and  similar  alloys  is  usually 
considered  in  three  grades:  A,  "High  Grade";  B,  "Inter- 
mediate1'; C,  "Brass  Special,"  according  to  the  amount  of  lead 
and  other  impurities  present.  A  fourth  grade,  D,  "Prime 
Western,"  contains  more  impurities  than  the  three  grades  preced- 

1  Mem.  Acad.  Arts  and  Sciences,  8,  Pt.  1,  May  20,  1850. 

2  Chem.  Eng.  9,  4. 

3  Year  Book,  1914,  pags  384;  also  personal  communications. 


254 


ANALYSIS  OF  COPPER 


ing.     In  1916,  a  new  "Selected  Grade,"  with   .80%   lead,  has 
been  proposed. 

HIGH  LIMITS. 


Grade 

A. 
High 

B. 

Interm. 

C. 

Special 

D. 

Western 

Lead 

Per  cent 
.07 

Per  cent 
20 

Per  cent 
75 

Per  cent 
1  50 

Iron. 

03 

03 

04 

08 

C  admiu.ni 

.05 

.50 

75 

? 

The  sum  of  lead,  iron  and 
cadmium  shall  not  exceed 
Aluminum  

.10% 
.00 

.50% 
.00 

1.20% 
.00 

? 

? 

ANALYSIS 

32.  Lead,  by  "Lead  Acid"  Method.  —  Weigh  into  a  350  c.c. 
beaker  25  grams,  15  grams,  10  grams,  or  5  grams  of  sa  wings  or 
drillings,  according  to  whether  the  spelter  is  of  grade  A,  B,  C,  or 
D,  respectively,  and  add,  according  to  weight  of  sample,  300  c.c., 
180  c.c..  120  c.c.,  or  60  c.c.  of  "lead  acid."     For  preparation  of 
lead  acid,  see  note.     When  all  but  one  gram  of  zinc  is  dissolved, 
filter  on  a  close  paper  and  wash  out  the  beaker  twice  with 
"lead  acid"  from  a  wash  bottle.     Wash  the  met  allies  back  from 
the  filter  to  the  original  beaker  with  water  and  dissolve  in  a  little 
hot  (1  : 1)  nitric  acid.    Add  40  c.c.  of  lead  acid,  and  evaporate 
to  strong  fumes  of  sulphuric  acid.    When  cool,  add  35  c.c.  of 
water  (which  is  the  quantity  of  water  evaporated  from  the  lead 
acid)    and   heat  to   boiling.      Add   the   first   filtrate  (containing 
most  of  the  zinc  and  possibly  a  little  lead),  stir  well,  and  settle 
at  least  five  hours,  filter,  wash  with  lead  acid,  then  with  a  solu- 
tion of  equal  parts  of  alcohol  and  water  and  finally  with  alcohol 
alone.     Ignite,  and  weigh  the  lead  sulphate  as  usual. 

NOTE.  —  "Lead  acid"  is  a  solution  of  one  volume  of  sulphuric 
acid  (d.,  1.84)  in  seven  volumes  of  water,  saturated  with  lead 
sulphate.  It  is  prepared  as  directed  in  the  first  part  of  this 
chapter  (3),  under  the  method  for  "lead  in  brass." 

33.  Lead,  by  Electrolysis.  —  Weigh  out  8.643  grams  of  the 
sample  into  a  400  c.c.  beaker  and  add  sufficient  water  to  cover 
the  sample.     Then  30  c.c.  of  concentrated  nitric  acid  (d.,  1.42) 
are  added  gradually  and  cautiously  until  solution  is  complete, 


THE  PRINCIPAL  COMMERCIAL  ALLOYS  OF  COPPER    255 

and  the  solution  is  boiled  for  a  few  minutes  to  dispel  the  nitrous 
fumes.  Wash  off  the  cover* glass  and  sides  of  the  beaker  and 
transfer  the  liquid  to^a  200  0*3.  electrolytic  beaker.  Dilute  to 
125  c.c.  and  electrolyze  with  a  current  of  five  (5)  amperes.  The 
time  required  for  the  electrolysis  is  from  J  to  f  of  an  hour, 
depending  on  the  amount  of  lead  present  in  the  sample.  Solu- 
tions are  tested  for  complete  precipitation  of  lead  by  washing 
down  the  cover  glasses  and  sides  of  the  beaker,  so  that  the  depth 
of  the  solution  is  increased  about  \  inch  (1.2mm.).  The  current 
is  then  continued  for  fifteen  minutes  and  if  the  newly  exposed 
surface  is  still  bright,  the  lead  is  completely  deposited.  The 
anode  is  then  washed  three  or  four  times  with  distilled  water, 
once  with  alcohol;  then  dried  in  an  oven  at  210°  C.  for  J  hour 
and  weighed. 

The  weight  of  the  lead  dioxide,  Pb02,  in  milligrams,  divided 
by  100  will  give  the  percentage  of  lead.  The  dioxide  deposit  can 
be  readily  removed  by  covering  the  anode  with  dilute  nitric  acid 
and  inserting  a  rod  of  copper. 

The  electrodes  recommended  by  the  Committee  are  cylinders 
of  platinum  gauze,  48  meshes  to  the  linear  inch  (or  18  per  cm.). 
The  anodes  are  1J  inches  (316  mm.)  in  diameter  and  of  equal 
height,  with  a  stem  4J  inches  (108  mm.)  long  of  16-gauge  wire, 
making  the  total  height  5J  inches  (or  14  cm.).  The  cathodes 
are  \  inch  (12.7  mm.)  in  diameter,  but  having  the  same  height 
and  length  of  wire  stem  as  the  anodes. 

34.  Iron.  —  Weigh  25  grams  of  zinc  into  a  tall  700  c.c. 
beaker  and  dissolve  cautiously  in  125  c.c.  of  nitric  acid.  Boil, 
dilute,  add  considerable  ammonium  chloride,  and  then  ammonia 
until  the  white  zinc  salts  have  dissolved.  Boil,  let  settle,  and 
filter  on  a  11  cm.  S.  &  S.  "black  ribbon"  filter  paper.  Wash 
with  dilute  ammonia  and  with  hot  water.  Dissolve  the  precipi- 
tated ferric  hydroxide  with  hot  (1  : 4)  sulphuric  acid,  add  40  c.c. 
of  (1:1)  sulphuric  acid,  pass  through  a  Jones  reductor,  wash 
first  with  150  c.c.  of  water,  then  with  100  c.c.  of  water,  and 
titrate  with  permanganate. 

The  potassium  permanganate  solution  contains  .2  gram  of  the 
crystals  per  liter.  One  c.c.  of  the  permanganate  will  equal 
.000334  grams  of  iron.  The  solution  is  standardized  against 
sodium  oxalate,  whose  correctness  has  been  guaranteed  by  the 
maker.  Weigh  out  duplicate  samples  of  sodium  oxalate,  weigh- 


256  ANALYSIS  OF  COPPER 

ing  .0200  gram.  This  will  take  between  49  and  50  c.c.  of  the 
permanganate  solution.  To  convert  sodium  oxalate  to  iron,  use 
the  factor  .8334.  Run  through  a  blank  using  the  same  amounts 
of  water  and  acid  and  deduct  from  the  tit  ration. 

NOTE.  —  If  before  passing  the  solution  through  the  reductor, 
a  large  amount  of  lead  sulphate  is  present,  it  is  well  to  filter  it 
off  to  prevent  it  from  clogging  the  reductor. 

i 
35.   Cadmium.  —  Weigh   25   grams   of   drillings   into   a   tall 

beaker;  add  250  c.c.  of  water  and  55  c.c.  of  concentrated  hydro- 
chloric acid  and  stir.  When  the  action  has  almost  ceased,  add 
more  acid  with  stirring,  using  about  2  c.c.  at  a  time,  and  allowing 
to  stand  after  each  addition  of  acid,  until  finally  all  but  about 
2  grams  of  the  zinc  have  been  dissolved.  About  60  c.c.  of  acid 
in  all  are  usually  required;  it  is  best  to  allow  the  first  55  c.c.  of 
acid  to  act  overnight.  Filter,  first  transferring  one  of  the 
undissolved  pieces  of  zinc  to  the  filter,  and  wash  a  couple  of 
times  with  water.  Discard  the  filtrate.  Wash  the  metallics  on 
the  filter  paper  back  into  the  500  c.c.  beaker,  cover,  and  dissolve 
in  nitric  acid.  Transfer  to  a  casserole,  add  20  c.c.  of  (1  :  1) 
sulphuric  acid  and  evaporate  to  fumes,  take  up  with  about  100 
c.c.  of  water,  boil,  cool,  and  let  settle  for  several  hours  (best  over- 
night). Filter  off  the  lead  sulphate  on  paper,  wash  with  water, 
retain  the  filtrate,  and  discard  the  lead  sulphate.  Dilute  the 
filtrate  to  400  c.c.,  add  about  10  grams  of  ammonium  chloride, 
and  pass  hydrogen  sulphide  into  the  liquid  for  one  hour.  It  is 
occasionally  necessary  to  start  the  precipitation  of  the  cadmium 
sulphide  by  the  addition  of  one  or  two  drops  of  ammonia  to  the 
dilute  solution.  Allow  to  stand  until  settled,  filter  off  the 
impure  cadmium  sulphide  in  a  loose-bottomed  Gooch  crucible; 
remove  the  cadmium  sulphide  by  carefully  punching  out  the 
bottom  into  a  200  c.c.  tall  beaker.  Wipe  off  any  adhering 
cadmium  sulphide,  using  a  little  asbestos  pulp,  add  60  c.c.  of 
(1  : 5)  sulphuric  acid,  and  boil  for  one-half  hour.  The  dilute  acid 
dissolves  cadmium  and  zinc  sulphides,  but  not  copper  or  lead 
sulphides.  Filter  and  dilute  to  300  c.c.,  add  2  grams  of  am- 
monium chloride,  and  precipitate  with  hydrogen  sulphide  in  order 
to  get  rid  of  traces  of  zinc.  Let  settle,  filter,  and  transfer  to  a 
platinum  dish,  cover,  and  dissolve  in  (1  : 3)  hydrochloric  acid. 


THE  PRINCIPAL  COMMERCIAL  ALLOYS  OF  COPPER    257 

Then  the  sulphide  remaining;  on  the  filter  paper  is  also  dissolved 
by  hot  (1:1)  hydrochloric  aci<J,  and  is  added  to  the  solution  in 
the  platinum  dish.  A  little  sulphuric  acid  is  added  and  the 
solution  is  evaporated  to  strong  fumes  of  sulphuric  acid.  It  is 
diluted  with  water,  a  few  cubic  centimeters  of  strong  nitric  acid 
are  added  to  oxidize  any  shreds  of  filter  paper,  and  the  solution 
is  again  evaporated  to  sulphuric  acid  fumes.  The  excess  of 
sulphuric  acid  is  removed  by  heating  the  dish  cautiously,  and 
finally  heating  nearly  to  redness,  and  the  cadmium  is  weighed  as 
sulphate. 

36.  Cadmium  by  Electrolysis.  —  Proceed  as  above  until  the 
purified  cadmium  sulphide  has  been  dissolved  in  hydrochloric 
acid.     Then   oxidize   with   nitric   acid   and   filter  from   sulphur. 
Transfer  the  solution  to  200  c.c.  electrolytic  beaker,  add  a  drop 
or  two  of  phenolphthalein  and  then  pure  sodium  or  potassium 
hydroxide  solution  until  a  permanent  red  color  is  obtained.     A 
strong  solution  of  pure  potassium  cyanide  is  then  added  with 
constant  stirring  until  the  precipitate  of  cadmium  hydroxide  is 
completely  dissolved.     Avoid  using  an  excess  of  the  potassium 
cyanide.     Dilute  the  solution  to  150  c.c.  and  electrolyze  with  a 
current  of  5  amperes,  using  the  same  size  gauze  electrodes  as  in 
the    "lead    determination."     Time,    one    to    two    hours.     The 
solution  should  always  be  tested  for  cadmium  as  follows :  -raise 
the  liquid  in  the  beaker  and  then  note  after  twenty  minutes  the 
newly   exposed   surface   of   the  electrodes.     If  still   bright,    the 
cadmium   is   completely   deposited.     Next   wash   the   electrodes 
with  distilled  water  and  then  with  alcohol.     Dry  at  100°  C.,  cool 
and  weigh.     The  increase  is  metallic  cadmium. 

37.  Special  Titration  for  Lead.  —  A  rapid  technical  assay  for 
lead  has  recently  been  described  by  E.  J.  Ericson.1     The  resi- 
dues from  the  solution  of  most  of  the  zinc,  obtained  as  in  the 
standard  method,  are  dissolved  in  10  c.c.  of  nitric  acid,  boiling 
to  the  disappearance  of  brown  fumes.     Then  add   100  c.c.   of 
water,  30  c.c.  of  ammonia,  and  5  to  10  grams  of   ammonium 
persulphate,    according    to    the    amount    of    residue.     Boil    five 
minutes,  settle  ten  minutes,  and  filter  quickly  through  double 
2  cm.  filters,  size  1  F.     Wash  four  times  with  hot  10  per  cent 
ammonia  and  five  times  with  hot  water.     Place  lead  back  in 

1  J.  Ind.  and  Eng.  Chem.  6, 401  (1913);  Eighth  Inter.  Congress  Appl  Chem. 
1,  184. 


258  ANALYSIS  OF  COPPER 

beaker,  add  25  c.c.  of  hydrogen  peroxide  (10  to  50  c.c.  U.  S.  P, 
acid  per  liter  plus  50  c.c.  concentrated  nitric  acid).  Stir  until 
dissolved,  add  15  c.c.  of  nitric  acid  (d.,  1.2)  and  75  to  100  c.c.  of 
water,  and  titrate  the  excess  of  hydrogen  peroxide  by  standard 
potassium  permanganate  (.568  gram  per  liter).  If  25  c.c.  of 
reagent  does  not  dissolve  all  the  lead,  double  the  quantity  and 
double  the  blank  analysis.  For  zinc  high  in  lead,  the  solution  is 
checked  against  a  standard  spelter,  tested  by  a  standard  method. 
38.  Separation  of  Cadmium  in  Trichloracetic  Acid.  —  This 
element  is  first  separated  from  most  of  the  zinc  by  hydrogen 
sulphide  as  in  the  standard  method  (35),  and  the  first  impure 
sulphide  of  cadmium  is  redissolved  in  hydrochloric  acid.  The 
solution,  after  filtering  off  traces  of  copper  or  lead  sulphides  and 
boiling  out  the  hydrogen  sulphide,  is  nearly  neutralized  with 
ammonia.  Trichloracetic  acid,  which  dissociates  less  than  min- 
eral acids,  is'  employed  for  the  separation  of  the  last  traces 
of  the  zinc  from  the  cadmium.  A  solution  of  8  grams  of  the 
acid  is  added  and  the  solution  diluted  to  200  c.c.,  and  charged 
with  hydrogen  sulphide.  The  remaining  operations  are  the  same 
as  in  the  standard  method  (35).  The  cadmium  may  also  be 
titrated  like  zinc,  in  routine  work.  Dissolve  the  filtered  sulphide, 
remove  sulphur  by  a  second  filtration,  oxidize  with  nitric  acid, 
dilute  and  titrate  with  potassium  ferrocyanide  in  the  same  way 
as  for  zinc,  adding  ferric  chloride,  citric  acid,  and  ammonia.  The 
ferrocyanide  may  conveniently  be  of  the  following  value,  —  1  c.c. 
equals  .0025  gram  of  Cd. 


B 
I 


PART  V 
PHYSICAL  TESTS  — GENERAL  INFORMATION 

CHAPTER  XV 

METALLOGRAPHY  OF  COPPER  AND  BRASS 

Purpose  of  Examination.  —  In  a  general  sense,  metallography 
signifies  the  investigation  and  description  of  the  structure  of  metals 
and  their  alloys,  or  is  a  science  which  determines  the  physical 
properties,  microscopic  appearance,  and  microstructure  of  an 
alloy,  then  ascertains  how  these  factors  are  related  to  the 
thermal  and  mechanical  treatment  of  the  metal  and  to  its 
chemical  composition,  finally  considering  the  influence  of  defec- 
tive treatments  or  of  chemical  impurities  upon  the  metal  during 
manufacture  and  use.1  The  microscope  aids  the  vision  to  detect 
the  finer  structure  and  the  camera  fixes  a  record  of  the  observa- 
tion. Etching  of  the  polished  surface  brings  the  more  refractory 
constituents  into  relie-f  and  develops  the  structure. 

As  such  tests  are  already  a  valuable  assistance  in  foundries, 
some  condensed  description  of  practical  metallography  will 
recommend  itself  to  those  who  are  introducing  microscopical 
examination  in  their  work.2  The  art  of  photography  must  always 
be  previously  acquired.  Many  good  treatises  are  accessible.3 
The  description  is  therefore  confined  principally  to  methods  for 
the  selection  and  preparation  of  samples  of  copper  and  its  alloys 
for  the  microscope,  adding  some  recommendations  on  special 
apparatus  and  its  manipulation.  The  photomicrographs  of 
alloys  and  formulas  for  etching  were  communicated  by  W.  H. 
Bassett. 

Crystallography.  —  When  metals  or  alloys  are  cooled  through 
the  critical  temperatures  or  points  at  which  structural  changes 

1  Le  Chatelier  &  F.  Osmond,  Metallographist,  1,  5,  18,  65. 

2  See  list  of  standard  works  in  closing  paragraphs. 

3  Modern  Picture  Making,  Eastman  Kodak  Co. 


260  ANALYSIS   OF    COPPER 

can  occur,  the  crystals  may  be  simple  but  are  usually  star-like  or 
dendritic  forms,  masses,  or  crystallites  with  a  vein  filling  of  the 
more  fusible  entectic  mixtures.  These  forms  are  broken  up  by 
rolling  or  hammering  and  highly  modified  by  quenching,  anneal- 
ing, or  special  reheating  above  critical  temperatures.  In  the 
cooling  of  non-ferrous  alloys  from  a  liquid  state,  there  is  a  pro- 
gressive separation  of  one  or  more  solid-solutions,  the  number 
formed  depending  on  the  chemical  composition  of  the  alloy  and 
its  heat  treatment.  There  are  also  some  differences  in  the  judg- 
ment of  observers  as  to  the  nature  of  the  changes  at  trans- 
formation points  in  the  cooling  curves.  The  crystalline  forms 
are  designated  by  the  signs  for  the  letters  alpha,  beta,  gamma, 
delta,  etc.1  (See  micrographs.) 

The  constituents  of  alloys  2  may  be  present  as  :  (1)  free  metals 
nearly  pure;  (2)  solid  solutions  of  one  metal  in  another  or  of  def- 
inite chemical  compounds  in  excess  of  metal;  (3)  eutectic  mixtures; 
(4)  definite  chemical  compounds  of  metals  with  metals  or  non- 
metals;  (5)  allotropic  modifications  of  1  and  4.  According  to 
Charpy,  the  points  of  transition  in  copper-zinc  alloys  correspond 
to  a  series  of  definite  compounds.  Tafel3  considers  that  one 
compound,  Cu2Zn3,  is  proved  and  possibly  CuZn.  Sheperd4 
holds  that  no  definite  compounds  are  formed  in  brasses,  but 
that  one  to  six  solid  solutions  are  possible  according  to  condi- 
tions. Also  that  in  bronzes,  five  solid  solutions  are  possible, 
and  that  some  alloys  with  much  tin  or  aluminum  may  contain 
the  compounds  Cu3Sn,  or  CuAl2.  With  solid  alloys  of  silver  and 
copper,  crystallites  of  silver  may  hold  1  to  7  per  cent  of  copper 
and  a  sensible  amount  of  arsenic  and  antimony  in  solid  solution,5 
while  copper  crystallites  may  contain  1  to  2  per  cent  of  silver, 
hence  such  crystallites  cannot  be  assumed  to  be  pure  elements. 

The  structure  of  refined  cast  copper,  when  cooled  directly 
from  the  molten  condition,  consists  of  primary  crystallites  of 
copper,  partly  surrounded  or  divided  by  thin  seams  filled  with  a 
mother  liquor  or  eutectic  mixture  of  copper  and  its  suboxide 
(Cu  +  Cu2O),  containing  3.45  to  3.5  per  cent  of  oxygen.  The 
amount  of  eutectic  increases  with  the  oxygen  and  addition  of 

1  Metallographist,  6,  145;  H.  M.  Howe,   Elect.  Chem.  and  Met.  Indust. 
7,  423.     H.  O.  Hofman,  Metallurgy  of  Copper,  Chapter  IV. 

2  J.  E.  Stead,  Metallographist,  5  (1902),  111. 

3  Metallurgie,  5  (190S\  349. 

4  J.  Phys.  Chem.,  8,  421.     Metallurgie,  1  (1904),  462;  5,  349;  10,  632. 

5  Metallographist,  1,  5,  18,  65.     Zt.  Anog.  Chem.  49  (1908),  289. 


METALLOGRAPHY  OF    COPPER   AND   BRASS  261 

oxidizable  metallic  impurities,  imtil  in  highly  oxidized  or  rabbled 
metal,  the  structure  becomes  coarje  or  indistinct  and  globules  of 
the  suboxide  appear  over*  the  surface  of  the  etched  section. 

1.  The  Selection  of  Samples.  —  It  is  advisable  to  orient,  or 
measure  and  record,  the  exact  position  of  each  face  of  each  test- 
piece  taken  from  copper  or  alloys,  with  reference  to  the  length 
and  diameter  of  the  casting,  wire,  or  plate.     Two  photomicro- 
graphs are  usually  taken  from  each  of  two  dissimilar  faces  of  the 
small  sawed  cube  or  plate,  selecting  one  parallel  to  the  surface 
set  or  the  longest  dimension  and  one  perpendicular  to  it.     In 
foundry  work,  separate  views  may  be  taken  for  tests  of  defective 
metal  with  a  magnification  at  the  eye-piece  of  about  25  and  60 
diameters  which  corresponds  to  a  magnification  of  about  33  and 
77  diameters  respectively,  as  measured  on  the  glass  plate,  or  fin- 
ished print.      From  25  to  100  diameters  are  the  usual  limits  for 
examination  for  physical   defects,  the  higher  powers  up  to  im- 
mersion objectives  being  reserved  for  critical  studies  of  individual 
crystals.      The  location  of  test-pieces  is  easily  accomplished  by 
observing  a  fixed  system  in  stamping  the  test  sample.     This  re- 
cords the  position  of  the  etched  faces  with  reference  to  the  speci- 
men and  the  length  and  width  of  the  finished  photomicrograph. 

To  secure  any  proper  knowledge  of  the  structure  of  cast 
metal,  samples  should  be  taken  near  the  center  of  the  casting, 
on  the  side  near  the  "chill"  and  at  top  and  bottom.  A  fair 
average  position  is  considered  to  be  just  to  one  side  of  the 
longest  median  line  with  the  upper  face  of  the  cube  one-half 
inch  below  the  upper  surface  and  far  enough  from  the  ends  to 
avoid  the  chilling  effect  of  the  mold.  Pieces  are  usually  taken 
from  a  plate  or  casting  with  a  band-saw  having  ten  teeth  to  the 
inch,  and  cooled  by  a  stream  of  water  or  a  blast  of  compressed 
air,  which  is  directed  upon  the  sample.  As  the  crystalline 
aggregates  appearing  upon  the  surface  of  cast  metal  are  very 
large  and  variable  for  reasons  specified,  the  only  way  to  learn 
much  of  value  is  to  accumulate  a  large  number  of  micrographs 
for  comparative  study,  having  all  the  physical  and  chemical 
data  recorded  upon  the  cards. 

2.  Polishing.  —  Good  levigated  powders  are  easily  purchased. 
They  may,  however,  be  prepared  from  calcined  ammonium  alum, 
commercial  flour  emery,  oxide  of  chromium  from  combustion  of 
ammonium  bichromate,  and  oxide  of  iron  from  the  calcination 


262 


ANALYSIS   OF   COPPER 


in  air  of  ferrous  oxalate.1  To  properly  classify  the  fine  powders 
by  levigation,  one-tenth  per  cent  of  nitric  acid  may  be  added  to 
the  water  to  dissolve  calcium  carbonate,  etc.  Stir,  pour  off,  add 
distilled  water,  repeat  several  times,  finally  adding  a  little  am- 
monia to  help  settling.  After  fifteen  minutes,  the  coarse  grains 
may  be  rejected,  in  one  hour  a  coarse  powder  settles,  in  four 


Fig.  17.  —  Polishing  Disc. 

hours  a  powder  for  iron,  while  as  much  as  eight  days  may  be 
required  to  settle  the  finest  powders. 

Treatment  of  Sample.  —  The  sample  is  cut  so  that  a  surface  J 
inch  (6  cm.)  to  J  inch  (12.5  cm.)  square  can  be  filed.  First  it  is 
filed  smooth  with  a  second  cut  file  and  then  cross-filed  with  a 
very  fine  flat  file  to  remove  the  first  file  marks.  The  polishing 
is  then  done  on  a  wheel  which  makes  at  least  1800  revolutions 
per  minute  and  has  cloth-covered  faces  against  which  the 
sample  is  held.  The  polishing  apparatus  of  Prof.  C.  R.  Hay- 
ward  illustrates  one  of  the  recent  designs  which  protects  the 
1  Chatelier  &  Schloesing,  Metallographist,  6,  291. 


METALLOGRAPHY    OF    COPPER   AND   BRASS  263 

operator  from  the  mud  produced  by  the  fine  stream  of  water 
with  which  the  wheel  is  fed  (EJg.  17).  Zimmerschied  and  Aston 
have  published  similaf  designs.1  A  disc  specially  recommended 
consists  of  a  brass  plate  with  a  half-inch  rim  and  filled  with  solid 
paraffine  wax.2 

The  first  polishing  is  usually  done  on  a  wheel  faced  with  canvas 
(such  as  8-ounce  duck),  using  a  paste  of  flour  emery  and  water, 
applied  with  a  brush.  Water  is  allowed  to  drip  on  the  wheel 
during  the  polishing.  The  sample  is  again  washed  and  applied 
to  a  wheel  covered  with  heavy  broadcloth  (such  as  cloth  for 
billiard  tables),  upon  which  fine  tripoli  and  water  is  used.  The 
sample  is  again  washed  and  applied  to  a  broadcloth,  or  wax- 
covered,  wheel  on  which  a  thin  paste  of  jeweller's  rouge  is  used. 
Great  care  is  taken  in  this  final  polishing  to  use  the  right  amount 
of  rouge,  and  the  wheel  is  moistened  slightly  from  time  to  time 
with  water  from  a  wash-bottle,  so  that  finally  the  sample  comes 
from  the  wheel  polished  free  from  scratches  and  quite  dry,  with 
no  streaks  of  rouge  on  the  polished  surface.  These  conditions 
give  the  best  results,  for  scratches  are  easily  seen  and  no  further 
washing  (with  the  possibility  of  scratching  the  sample)  is 
necessary.  If  the  sample  is  one  of  cast  copper  containing 
oxygen,  this  method  of  finishing  will  bring  out  the  oxide  structure 
and  but  very  little  etching  is  then  necessary  to  prepare  it  for  the 
microscope. 

3.  Etching.  —  The  etching  of  all  samples  of  copper  and  brass 
is  done  in  a  mixture  of  hydrogen  peroxide  (perhydrol)  and 
ammonia.  Different  mixtures  are  used  for  different  copper 
content.  (J.  O.  Handy  has  proposed  to  etch  cast  copper  by  a 
solution  of  ferric  chloride  in  alcohol.) 

Cast  copper  (containing  oxygen)  is  taken  as  polished  clean, 
without  washing,  held  in  platinum-tipped  forceps  and  immersed 
with  a  stirring  motion  in  a  solution  containing  5  parts  by  volume 
of  ammonia  (d.;  .90),  5  parts  water,  and  2  parts  of  Marchand's 
hydrogen  peroxide.  (If  the  3  per  cent  peroxide  of  medical 
strength  must  be  employed,  omit  the  water.)  Stirring  is  con- 
tinued until  the  solution  ceases  to  effervesce.  The  sample  is 
then  washed  with  water,  wiped  with  clean  soft  cotton,  dipped 
in  alcohol  if  preferred,  and  dried.  Wrought  copper,  either  hard 

1  /.  Am.  Chem.  Soc.  29,  855,  and  Elect.  Chem.  and  Met.  Indust.  8,  15. 

2  Eng.  90,  108. 


264  ANALYSIS   OF   COPPER 

or  annealed,  is  etched  in  the  above  manner,  but  using  equal 
parts  of  water,  ammonia,  and  (M)  hydrogen  peroxide.  These 
proportions  are  not  absolute,  but  are  varied  as  experience  and 
conditions  indicate. 

Brasses  containing  85  per  cent  to  95  per  cent  copper  are 
etched  in  exactly  the  same  way  as  wrought  copper.  Brasses 
containing  63  per  cent  to  80  per  cent  copper  are  etched  in  a 
mixture  of  5  parts  ammonia,  5  parts  water,  and  2  parts  of  (M) 
hydrogen  peroxide  until  the  solution  begins  to  effervesce  (about 
3  to  5  seconds'  immersion).  There  is  no  definite  point  between 
80  per  cent  and  85  per  cent  copper  at  which  either  of  the  above 
mixtures  must  be  used  instead  of  the  other  one  described. 
High  brass,  containing  less  than  62  per  cent  copper,  is  first 
etched  by  electrolysis  in  a  solution  of  ferrous  sulphate,  sodium 
sulphate,  and  sulphuric  acid  made  up  as  follows :  Dissolve  30 
grams  of  ferrous  sulphate  (FeSO4)  and  4  grams  of  sodium 
hydroxide  (NaOH)  in  100  c.c.  of  water,  then  add  2000  c.c.  of 
water  and  100  c.c.  of  strong  commercial  sulphuric  acid.  The 
sample  is  held  in  platinum-tipped  forceps  hung  on  an  electrolytic 
stand  so  that  the  sample  just  fails  to  touch  the  solution.  By 
shaking  the  solution,  it  is  made  to  touch  the  sample  and  the 
surface  tension  keeps  this  contact.  The  sample  should  not  be 
dipped  in  the  solution,  but  should  be  held  so  that  the  surface 
of  the  solution  rises  slightly  to  meet  it.  If  the  sample  is  im- 
mersed, the  etching  is  not  uniform.  A  current  of  about  .1 
ampere  at  8  to  10  volts  is  necessary. 

"  Alpha  and  Beta"  Constituents.  —  The  "Beta"  constituent  in 
these  brasses  is  colored  reddish-brown  by  the  electrolytic  etching 
in  about  thirty  seconds,  but  the  "Alpha"  constituent  is  not 
affected.  These  brasses  become  covered  with  a  dark  coating 
which  can  be  wiped  off  with  wet  cotton.  The  sample  is  then 
washed  with  water  and  immersed  in  peroxide  mixture  (5:  5:  2) 
for  a  very  short  time,  washed  in  water,  dipped  in  alcohol,  and 
dried.  Brasses,  consisting  of  pure  "Beta"  crystals  only,  etch 
best  in  the  peroxide  mixture  just  given.  Only  when  "Alpha" 
and  "Beta"  crystals  occur  together,  is  it  necessary  to  etch  both 
by  electrolysis  and  hydrogen  peroxide  mixture.  German  silvers 
are  etched  by  electrolysis  alone  and  seem  to  etch  best  in  an  old 
solution,  i.e.,  one  that  is  becoming  saturated  with  dissolved 
metals  from  previous  etching  of  brasses. 


METALLOGRAPHY    OF    COPPER    AND   BRASS 


265 


Coppers,  brasses,  or  bronzes  -may  be  heat-tinted  in  the  final 
polishing  with  rouge  by  allowingjbhe  wheel  to  run  finally  dry  and 
become  hot  under  the  Specimen.  Practice  is  necessary  to  gauge 
the  amount  of  dryness  and  pressure.  Polishing  in  relief  is  also 
accomplished  by  long  polishing  with  tripoli  and  rouge  with  a 
soft  backing,  or  by  heating  copper  in  a  current  of  pure  hydrogen 
for  3  to  4  minutes  (6). 

For  the  new  product,  copper-clad  steel,  J.  0.  Handy  rec- 
ommends a  boiling  25  per  | _^ 

cent     solution    of    potassium 
cyanide. 

4.  Apparatus  for  Photo- 
micrographs. —  There  are  a 
number  of  good  types  in  use 
in  the  United  States  and 
Europe.  The  one  used  by  the 
author  is  designed  by  Sau- 
veur  and  Boylston  with  a 
Bausch  and  Lomb  microscope. 
For  copper  and  brass,  the 
usual  combination  of  lenses 
desired  in  American  micro- 
scopes consists  of  eye-pieces  of 
(25,  50,  75  mm.)  focal  length, 


Fig.  18.  —  Movable  Stage  with 
Magnetized  Holder. 


combined  with  a  series  of 
(16,  8,  4,  2  mm.)  objectives, 
or  a  series  of  objectives  ac- 
cording to  the  (J,  J,  J,  and  TV  inch)  system  of  focal  lengths. 

The  sample  is  illuminated  usually  by  a  small  prism  or 
glass  disc  mounted  within  the  lower  part  of  the  microscope  just 
above  the  objective.  Light  from  a  small  arc  lamp  with  auto- 
matic feed  passes  through  the  side  of  the  microscope  and  is  re- 
flected down  upon  the  upper  surface  of  the  specimen  by  turning 
the  milled  head  so  that  the  disc  sets  at  an  angle  of  about  45 
degrees.  A  movable  mechanical  stage  is  almost  a  necessity.  A 
small  magnetized  holder  is  convenient  for  iron  and  steel.  See 
Fig.  18. 

The  small  arc  lamp  usually  furnished  is  supplied  with  direct 
current  from  an  ordinary  wall  socket  through  a  special  resistance 
coil.  The  light  passes  through  condensing  lenses  and  a  cooling 


266  ANALYSIS   OF    COPPER 

cell,  containing  water  and  sufficient  potassium  chromate,  or  dichro- 
mate,  to  produce  a  pale  yellow  light  with  perhaps  a  greenish 
tint.  An  iris  diaphragm  shutter  is  placed  in  front  of  the  lamp 
and  a  short  distance  from  the  microscope.  For  visual  examination 
a  piece  of  cobalt  blue  glass  may  be  inserted  back  of  the  shutter. 

5.  Photography.—  " Hammer  Slow"  plates,  " Cramer's  Iso- 
chromatic,"  or  any  other  American  or  European  plate  of  slow 
speed  and  with  the  quality  of  non-halation,  may  be  employed 
and  the  exposure  will  vary  from  two  to  sixty  seconds  or  more, 
according  to  the  sample  and  the  amount  of  potassium  chromate 
or  dichromate  in  the  water-cooling  cell  of  the  electric  lantern. 
The  plates  may  be  developed  with  any  hydroquinone  (or  metol- 
hydro)  developer,  either  separately  or  in  a  developing  tank  and 
fixed  with  a  solution  of  sodium  thiosulphate  containing  a  little 
hardener.  The  tank  method  is  said  by  one  operator  to  give  the 
finest  negatives  when  the  right  conditions  have  been  learned. 
The  final  prints  are  usually  made  on  a  rapid  paper,  such  as 
Velox,  by  exposure  in  the  dark  room  to  the  light  of  a  tungsten 
lamp  and  finished  according  to  manufacturers'  formulas.  The 
papers  may  then  be  rolled  upon  squeegee  plates  of  japanned 
metal,  if  the  smooth  finish  is  preferred.  The  dry  prints  may 
be  easily  cut  to  uniform  .size  by  placing  them  on  a  soft 
wood  block  and  stamping  them  with  a  steel  die  which  is 
struck  with  a  copper  hammer.  The  small  circles  or  squares 
are  then  mounted  on  stiff  glazed  cards.  On  the  face  of  the 
cards,  a  printed  form  may  be  arranged  in  small  neat  type,  to 
be  filled  in  with  the  number  of  the  specimen,  the  conditions  of 
exposure,  degree  of  magnification,  position  of  the  sample,  and 
any  analytical  data  required  for  a  proper  understanding  of 
the  subject  photographed. 

In  order  to  show  the  general  structure,  or  crystalline  aggre- 
gates, in  cast  copper  and  also-  the  internal  structure  of  copper 
and  eutectic,  it  is  desirable  to  photograph  the  etched  faces  of 
cast  copper  with  a  low  and  a  high  power.  The  first  combination 
used  by  the  authors  gives  a  magnification  of  25  diameters  at  the 
eye-piece  or  about  33  diameters  on  the  4x5  inch  glass  plate  in 
the  holder.  To  determine  the  actual  magnification,  a  photo- 
graph may  be  taken  of  a  micrometer  scale,  or  an  image  of  the 
scale  may  be  formed  on  the  ground  glass,  and  the  distance  of 
the  lines  measured  on  the  plate. 


METALLOGRAPHY    OF    COPPER    AND   BRASS 


267 


Polished  samples  are  mounted  for  the  visual  examination  on 
a  cover  glass  slide  with  a  piege  of  wax,  or  in  a  special  holder. 
The  face  should  be  v^ery  carefully  leveled  until  it  is  exactly  at 
right  angles  to  the  axis  of  the  microscope.  As  already  indicated, 
this  instrument  should  be  furnished  with  a  movable  stage 'which 
permits  an  immediate  examination  of  the  whole  surface  in  order 
to  select,  in  the  case  of  copper  particularly,  an  average  structure 
for  exposure.  The  focussing  of  the  image  upon  the  ground  glass 
of  the  plate-holder  must  be  necessarily  very  sharp  or  exact,  and 
can  only  be  determined  by  experiment.  The  sensitized  plates  are 
exposed  to  the  yellow  light  of  the  illuminator  from  two  to  sixty 
seconds  according  to  the  subject,  a  matter  determined  also  by 
experience.  The  plates  should  then  be  developed  as  soon  as 
possible  by  regular  photographic  methods,  producing  as  sharp 
contrasts  and  clear  detail  as  possible. 

A  set  of  photomicrographs,  furnished  by  W.  H.  Bassett,  will 
illustrate  the  average  types  of  commercial  alloys  and  the  appear- 
ance of  good  finished  prints.  Some  structures  of  copper  x  are 
also  included  to  show  the  marked  differences  between  native 
mass  copper  and  cast  or  rolled  refined  metal. 

INDEX  TO  PHOTO-MICROGRAPHS  (MAGNIFIED  77  DIAMETERS) 


No. 

Name 

Condition  and  Heat 
Treatment 

Copper 
Silver 

Zinc 

1 
Ib. 

Copper 
Deoxidized 

Deoxidized 

Native    mass.     Also    by    cast 
copper  melted  under  charcoal. 
Remelted    and   hard-rolled,   re- 
fined 

Per  cent 
99.97+ 
99  976 

Per  cent 

2 
3 
4 

Half  circle 
(with  3) 
(with  2) 

Cast  copper 

Hard-rolled  refined,  .072"  thick. 
Heated      i       hour     600°       C., 
quenched  
High  pitch  refined  ingot  

99.927 

99.927 
99.945 

.... 

5 
6 

Brass 

ii 

Hard-rolled  from  800°  C  
Heated       |      hour     600°       C., 
quenched  

89.96 
u 

10.04 
(i 

7 
8 
9 
10 
11 

tt 

u 

u 

Hard  brass 
(same  as  10) 

Heated  as  above,  quenched  .  .  . 

it                (t                U                              11 
((               {(               ((                           (C 

Finished  hard  
Heated       £       hour    650°    C., 
quenched  

80.18 
66.08 
60.63 
56.25 

u 

19.82 
33.92 
39.37 
43.75 

u 

12 

(like  10) 

Heated    as    above,  but    slowly 
cooled  .    .                              \ 

u 

(i 

Prepared  by  A.  W.  Senter. 


268  ANALYSIS   OF   COPPER 

6.  Determination  of  Oxygen  in  Copper  by  Photomicrographs. 

—  Following  several  earlier  attempts  to  estimate  oxygen  by 
planimetric  measurement  of  the  relative  areas  of  copper  and 
eutectic  in  a  microscopic  field,  E.  S.  Bardwell  has  avoided  such 
a  tedious  measurement  by  projecting  the  area  of  the  field  on  a 
piece  of  paper  and  tracing  the  copper  areas.  The  areas  are  then 
cut  out  with  a  shears  and  weighed.  (See  15,  Chapter  XIII.) 

7.  Special  Tests  with  Etched  Samples.  —  (a)  Determination  of 
Hardness  of  Micrographic  Structures.1  —  For  the   scratching  of 
etched   sections,   one  metallographist   employs  a  set  of   needles 
standardized  to  Moh's    mineral    scale.     The    principal  numbers 
are:   lead,    1;    tin  with   iron,   2;   zinc,   2.5;    copper,   3;    bronze 
with  12  per  cent  tin,  3.5;  iron  wire,  3.7  to  3.9;  sewing  needles, 
5  to  5.5;    tempered  yellow,   4;  blue,   5;    drill  steel  yellow,   6; 
chrome    steel,    6  to   6.5;    ferrochrome,    7    to  7.5°    of  hardness. 
Constituents  may  also  be  identified  by  color  and  behavior  to 
reagents.     The  schleroscope  or  Brinell  machine  are  now  advo- 
cated and  employed  for  working  tests  of  metals. 

(b)  Preservation  of  Etched  Specimens.  —  The  etched  faces  may 
be  carefully  painted  with  a  thin  solution  of  jeweller's  lacquer.     A 
special  varnish  which  is  recommended,  known  as  Zapon,  is  a 
solution  of  guncotton  in  amyl  acetate.     It   permits   the  use   of 
lenses  of  the  highest  power  without  removal  of  the  coating  (Le 
Chatelier) . 

(c)  Casting  of  Small  Specimens.  —  Small  specimens  of  experi- 
mental alloys  may  often  be  melted  in  magnesia  crucibles    and 
cooled   under   charcoal,    or  cast  on  plate  glass  or  steel.      When 
glass  gives  too  much  trouble,  such  alloys  may  be  cast  on  sheet 
mica.2    Cut  a  funnel  of  good  charcoal  of  the  size  of  button,  de- 
sired, place  it  on  a  fresh  sheet  of  mica,  and  pour  in  the  alloy. 
Place  the  mold  and  metal  on  a  fresh  sheet,  cover  with  some 
potassium  cyanide,  heat  with  a  flame  until  upper  surface  of  the 
metal  softens,  and   quickly  press  down  a  third  sheet  upon  the 
top  of  the  alloy  in  order  to  obtain  a  good  surface  for  polishing. 

(d)  Determination  of  the  Weakest  Structure. — The  weakest  part 
of  a  metal  or  alloy  can  be  often  ascertained  by  bending  the 
etched  microscopic  section  itself.     This  can  be  effected  by  pla- 
cing the  section,  polished  side  down,  over  a  V-space  cut  out  of  a 

1  Method  of  Behrens,  Metallographist,  6,  158. 

2  Method  of  H.  J.  Hannover,  Ibid.  4,  29.  — Le  Chatelier  p.  17. 


PLATE  I 


Fig.  1 


..Sv  */l-  T^A. "-' ,    *     "iM^j^^L  -      ^'.JM^feJ^  **I^t 


PLATE  II 


Fig.  7 


EGKp'fi 

Et-.JV^-lt 


W*^£m 


Fig.  8 


Fig.  11 


Fig.  12 


METALLOGRAPHY   OF    COPPER   AND   BRASS  269 

solid  piece  of  steel  and  applying  force  to  the  back  to  bend  the 
specimen.  Even  if  the  piece  dogg  not  break  off,  the  weak  places 
often  give  way  and  it*is  easy  to  detect  the  zone  of  incipient 
fracture  by  examination  under  the  microscope.1 

NOMENCLATURE  —  COMMON  TERMS 

Allotropic  Modification  signifies  a  change  from  the  normal 
chemical  and  physical  properties  of  a  substance  without  any 
actual  change  in  the  composition.2 

Alloy,  Metallic.  —  An  intimate  mixture  or  union  of  metallic 
substances  which  on  melting  do  not  separate  into  distinct  liquid 
layers  (Stead). 

Alpha  State.  —  A  term  which  has  been  applied  by  metallogra- 
phists  to  the  first  type  of  solid  solutions  which  may  separate  as 
crystals  in  the  cooling  of  brass  and  other  non-ferrous  alloys.' 
Not  colored  by  acid  electrolytic  etching,  a  characteristic  struc- 
ture in  (alpha)  brass,  63  per  cent  copper  and  in  bronze  with 
less  than  10  per  cent  of  tin.  See  micrographs. 

Atomic  Volume.  —  The  atomic  weight  of  an  element  divided 
by  its  specific  gravity. 

Beta  State.  —  The  name  is  used  with  non-ferrous  alloys  to 
designate  a  second  type  of  solid  solution  which  may  be  formed 
as  crystals  in  brass,  etc.,  during  cooling  or  by  heat  treatment;  — 
colored  by  acid  etching.3 

Critical  Point.  —  The  point  or  zone  of  temperature  at  which 
some  physical  or  chemical  change  takes  place  in  the  cooling  or 
heat  treatment  of  a  metal  or  alloy.  Sometimes  indicated  by 
evolution  or  absorption  of  heat. 

Eutectic.  —  The  solidified  mother  liquor,  produced  in  the  cool- 
ing and  crystallization  of  metals,  having  a  freezing  point  below 
that  of  either  of  the  constituents. 

Eutectic  Point.  —  The  point  of  intersection  of  two  inclined 
branches  and  a  horizontal  line  in  the  freezing  point  curve  of 
metals  with  temperatures  and  percentage  of  constituents  as  co- 
ordinates. The  horizontal  line  is  called  the  eutectic  line,  and 
the  alloy  the  eutectic. 

1  Due  to  J.  E.  Stead. 

2  Nomenclature  of  Microscopic  Substances,  etc.,  in  Steel,  Int.  Soc.  for 
Testing  Materials,  1914. 

3  Inst.  Metals,  2  (1909),  1.    Metallurgie,  1  (1904),  462. 


270  ANALYSIS   OF   COPPER 

Eutectoid.  —  The  eutectoid  is  analagous  to  the  eutectic  in 
almost  every  way,  differing  from  it  simply  in  that  the  eutectoid 
point  represents  the  intersection  of  two  lines  along  which  separa- 
tion has  taken  place  from  a  solid  solution  rather  than  from  a 
liquid  melt.1 

The  eutectoid  is  the  alloy  of  lowest/  transformation  point.2 

Gamma  State.  —  The  terms,  alpha,  beta,  gamma,  delta,  etc., 
have  all  been  applied  to  the  solid  solutions  and  mixtures  suc- 
cessively formed  in  the  cooling  of  brass  and  bronze  from  a 
liquid  melt  or  by  reheating  and  quenching  in  water.  Consult 
standard  references.  Constituents  a  and  /3  are  ductile  and  malle- 
able, but  7,  6  (also  e  and  TJ  if  accepted)  are  increasingly  brittle. 

Isomorphous.  —  A  term  applied  to  crystals  of  similar  form, 
or  to  a  mixture  crystallizing  as  a  homogeneous  whole. 

Metarals.  —  Metallographists  now  define  microscopic  sub- 
stances in  two  general  classes:  First,  "metarals,"-  —  single  phases, 
such  as  elements,  chemical  compounds,  or  solid  solutions;  second, 
" aggregates"  or  mixtures  in  the  definite  proportions  of  eutectics 
and  eutectoids,  or  of  indefinite  proportions.  In  minerals,  obsidian 
is  a  type  of  a  solid  solution,  while  mica,  feldspar,  and  hornblende 
are  aggregates. 

Slip-bands.  —  A  microscopic  appearance  in  smooth  surfaces 
of  strained  metals  caused  by  slips  along  the  cleavage  or  gliding 
planes  of  the  crystalline  grains. 

Solid  Solutions.  —  Solid  "isomorphous  mixtures"  or  " mixed 
crystals"  of  two  or  more  substances,  such  as  gold  and  silver,  or 
copper  with  nickel,  —  metarals. 

ADDITIONAL  REFERENCES 

Microscopic  Analysis  of  Metals,  Osmond  and  Stead,  1904. 

Metallography,  Desch,  London. 

Metallographie,  Heyn  and  Bauer,  Leipzig. 

Metallographie,  Guertler. 

Introduction  to  Metallography,  Goerens,  translated  by  Ibbotson. 

Metallography  of  Iron  and  Steel,  Sauveur. 

Application  to  Foundry  Work,  Sauveur,  Iron  and  Steel  Magazine,  9,  also 
10,  29,  319,  413,  and  11,  119. 

Structure  of  Metals  and  Binary  Alloys,  Wm.  Campbell,  Metallographist, 
6,  25.  Metallurgy  of  Copper,  Hofrnan,  Chapter  IV  (best  review). 

Microscopic  Study  of  Metallic  Alloys,  G.  Charpy,  Ibid.  1,  87-192. 

Microstructure  of  Bronzes,  Metallographist,  1,  150. 

Alloys  of  Arsenic  and  Copper,  Roberts-Austen,  Metallographist,  1,  342. 

1  Introduction  to  Physical  Metallurgy,  Rosenhain. 

2  Howe  and  Levy,  Report  IL,,  Vol.  2,  6th  Int.  Congress  for  Test.  Materials. 


METALLOGRAPHY   OF   COPPER   AND   BRASS  271 

Stahl,  Photomicrographs  of  Copper,  Met.  6,  (1909),  609. 

Copper  and  Arsenic,  Bengough  and  Hill,  Inst.  Met.  3  (1910)  34. 

Special  Brasses  and  the  Quenching  of  Bronze,  L.  Guillet,  Iron  and  Steel 
Magazine,  10,  29;  11,  124.  Rev.  Met.  6  (1909)  1251,  — 10  (1913),  769,  1130. 

Metallography  of  Gun  Metal,  H.  S.  Primrose,  Met.  and  Chem.  Eng.  8, 
561,  and  Eng.  90,  (1910),  446  — from  Jour.  British  Inst.  of  Metals. 

Reports  of  British  Alloys  Research  Committee,  Eng.  Magazine,  1904 
et  seq. 

Heat  Treatment  of  Brass,  Carpenter  and  Edwards,  J.;  Inst  Met.  4  (1910) 
92;  5,  127;  8  (1912),  51. 

Copper  and  Brass,  H.  Baucke  HH  —  C.  Grard  IIi5,  6th  Int.  Congress  for 
Test.  Materials. 


CHAPTER  XVI 
THE  ELECTRICAL  RESISTIVITY   OF   COPPER 

MANUFACTURERS  and  consumers  of  copper  know  that  very 
slight  traces  of  some  impurities  have  a  most  marked  effect  in 
lowering  the  percentage  of  electrical  conductivity,  or  increasing 
the  electrical  resistivity  of  refined  copper.  For  "Lake"  copper 
(whose  only  notable  impurity  is  arsenic),  and  for  refined  elec- 
trolytic brands,  the  test  of  the  conductivity,  or  resistivity,  of 
the  annealed  wire  furnishes  a  rapid  approximate  determination 
of  the  arsenic  (and  antimony),  which  enables  an  operator  to 
grade  the  metal  and  permit  it  to  be  delivered  only  for  work  in 
which  that  particular  grade  of  metal  can  satisfy  the  requirements. 

1.  Apparatus  for  Measurement  of  Resistivity.  —  The  types 
of  low  resistance  "bridges"  employed  in  mills  and  refineries  are 
so  varied  in  design  and  being  so  rapidly  improved,  that  a  de- 
scription of  anything  but  the  latest  form  is  inadvisable.  In 
Germany,  a  Thomson  bridge  designed  by  Siemens  &  Halske  is 
employed,  the  standard  slide  wire  being  made  of  German  silver 
with  a  total  resistance  of  .1  ohm.  The  percentage  conductivity, 
hitherto,  has  been  compared  with  the  value  for  pure  mercury 
given  by  the  Reich  Anstalt. 

In  America,  more  than  twenty  firms  use  a  Hoope's,  or 
Willyoung,  instrument,  in  which  a  piece  of  copper  wire  about 
1  meter  in  length  is  compared  directly  with  copper  standards 
whose  resistance  has  been  determined  by  the  U.  S.  Bureau  of 
Standards.  A  new  form  of  a  direct-reading  conductivity  bridge 
is  the  design  of  G.  Grower  of  the  American  Brass  Co.,  and 
made  by  Leeds  &  Northrup  of  Philadelphia.  The  wire  is  cut 
to  a  fixed  length  of  68.26  cm.  before  weighing  and  it  is  only 
necessary  to  subject  the  scale  reading  of  conductivity  to  a 
correction  for  the  percentage  of  variation  of  the  sample  from  a 
standard  weight  of  20  grams. 

The  machine  is  less  expensive  than  some  other  types,  because 
it  is  only  required  to  test  the  one  size  (.080  inch  in  diameter), 


THE   ELECTRICAL   RESISTIVITY   OF    COPPER          273 

which  has  been  adopted  as  $  standard  size  for  comparative  tests 
by  the  principal  American  producers  and  consumers,  and  is 
prescribed  in  the  copper  specifications  of  the  American  Society 
for  Testing  Materials.1 

2.  Density.  —  The   " density"   of  copper  is  defined   by  the 
U.  S.  Bureau  of  Standards  to  be  "the  number  of  grams  per 
cubic  centimeter,"  and  is  identically  equal  to  the  "specific  grav- 
ity" of  the  copper  at  20°   (or  other  specified  temperature),  re- 
ferred to  water  at  its  maximum  density.     This  point  is  found 
at  4°  C.,  at  which  degree  a  cubic  centimeter  of  water  weighs 
one  gram.     Example  :    A  specific  gravity  of  8.914   at  20°  C.  is 
equal  to  a  density  of  8.8986.    The  value  assumed  by  recent  au- 
thorities is  8.89  for  either  hard-  or  soft-drawn  wire.    The  average 
density  of  cast  copper  is  about  8.55,  but  with  native  mass,  or 
deoxidized    copper  melted   in    crucibles,  the   value   is   8.925   to 
8.935.     Annealing  shortens  a  rod  or  wire  without  changing  the 
apparent  density. 

3.  Resistivity.  —  This  term,   as  generally  adopted,   signifies 
the   electrical   resistance   in   international   ohms   of   1   meter   of 
wire  weighing  1  gram,  or  resistance  per  "meter-gram,"  measured 
at  the   standard   temperature   of  20°  C.     This  is   obtained   by 
multiplying  the  weight  of  one  meter  of  the  wire  by  the  elec- 
trical resistance   of   one   meter   at   20°  C.,    calculated   from-  the 
observed  resistance  of  the  length  of  sample  actually  tested.    The 
value  for  the  resistivity  of  copper  wire  assumed  to  have  100 
per    cent    conductivity,    was    first    accurately    determined    by 
Matthiesen  in  1860,  but  copper  wire  is  now  produced  testing 
102  per  cent  conductivity,  and  native  mass  or  cathodes  may  test 
up  to  103  per  cent  by  his  standard.     See  table  of  data  on  the 
next  page. 

As  resistance  measurements  cannot  be  made  at  a  fixed  tem- 
perature in  practice,  it  is  necessary  with  a  German  silver  stand- 
ard to  reduce  the  observations  to  the  standard  temperature  of 
20°  C.,  or  whatever  value  is  assumed  as  standard.  When  the 
bridge  standard  is  an  annealed  copper  wire  of  nearly  100  per 
cent  "conductivity,"  no  temperature  correction  is  necessary  in 
tests  of  high-grade  metal  of  97  per  cent  "conductivity,"  or 
better.  When  arsenical,  or  low-grade  casting  metal  is  tested 
at  variable  temperatures  against  a  fixed  copper  wire  standard 
1  Year  Book,  1914. 


274  ANALYSIS   OF    COPPER 

of  100  per  cent  conductivity,  it  is  necessary  to  apply  a  correc- 
tion to  reduce  the  reading  to  the  standard  temperature  of  the 
bridge.  A  table  of  corrections  may  be  determined  for  each 
instrument  by  cooling  the  testing  room  in  winter  down  to  the 
freezing  point  and  testing  a  set  of  copper  wire  samples  which 
will  cover  the  material  ordinarily  tested.  These  tests  are  re- 
peated on  the  same  samples  as  the  temperature  rises  through  a 
range  of  50°  F. 

4.  Temperature  Coefficient.  —  The  U.  S.  Bureau  of  Stand- 
ards has  determined  that  the  temperature  coefficient  of  electrical 
resistance  is  proportional  to  the  electrical  conductivity  of  copper, 
for  values  over  97  per  cent.1  The  author  has  determined  by  the 
above  method  that  the  value  for  temperature  coefficient  is  also 
true  for  wire  produced  from-  furnace-refined  copper,  down  to  a 
limit  of  30  per  cent  conductivity,  or  even  less,  when  the  prin- 
cipal impurity  is  arsenic.2  In  other  words,  the  coefficient,  which 
the  Bureau  assumes  to  be  .00394  per  degree  Centigrade,  is  strictly 
proportional  to  the  " conductivity"  by  Matthiesen's  standard 
whatever  the  purity  of  the  copper.  This  is  probably  true  for 
electrolytic  copper,  which  contains  traces  of  other  impurities, 
such  as  antimony. 

CALCULATION   OF  RESISTIVITY 

5.  Rule  1.  —  A  resistance  R  at  temperature  t  is  corrected  to 
the  standard  temperature  of  20°  C.  by  applying  the  tempera- 
ture coefficient  at  20°  C.  (termed  C2o)  in  the  formula : 

Rt  =  #20(1  +  CaO  ~  20]). 

This  coefficient  applies  only  to  20°  as  a  standard.  For  the  cal- 
culation of  coefficients  to  other  specified  temperatures,  see  refer- 
ence (1).  The  (20°)  temperature  coefficient  for  copper  of  100  per 
cent  conductivity  is  .00394  per  degree  Centigrade,  according  to 
the  U.  S.  Bureau  of  Standards. 

Rule  2.  —  The  Bureau  also  shows  the  relation  between  the 
percentage  of  electrical  conductivity  and  temperature  coefficient 
and  the  reduction  of  resistivity  to  standard  temperature  by  the 
following  statement :  The  change  of  resistivity  (not  resistance) 

1  J.  H.  Bellinger,  Reprint  147,  Bull.   U.  S.  Bureau  of  Standards,  Vol.  7, 
No.  1. 

2  Circular  31,  U.  S.  Bureau,  Copper  Wire  Tables  (1912). 


THE   ELECTRICAL   RESISTIVITY   OF    COPPER  275 

per  degree  Centigrade  of  a,  sample  of  copper  is  .000598  (inter- 
national) ohm  per  meter-graig,  or  .00681  micro-ohm  per  Centi- 
meter cube. 

Rule  3.  —  The  resistivity  in  international  ohms  corresponding 
to  100  per  cent  conductivity,  Matthiesen  standard,  was  fixed  at 
.153022  by  the  American  Institute  of  Electrical  Engineers  and  the 
U.  S.  Bureau  of  Standards.  Within  the  last  two  years,  Govern- 
ment Bureaus  have  agreed  upon  a  new  value,  .15328,  which  is 
about  .17  per  cent  lower,  if  calculated  in  terms  of  conductivity. 
The  tendency  with  large  concerns,  at  present,  is  to  report  specifi- 
cations to  outside  parties  in  terms  of  "  resistivity,"  rather  than 
the  debatable  value  of  "  conductivity." 

The  percentage  "  conductivity "  of  a  sample  of  copper  by 
length  and  weight,  or  meter-gram  system,  is  obtained  by  divid- 
ing .153022  (or  the  latest  international  value  of  .15328)  by  the 
"resistivity"  of  the  sample  tested. 

6.  Notes  on  the  Determination  of  Resistivity  of  Wire.  - 
Until  comparative  investigations  by  the  Government  Bureau 
and  leading  copper  concerns  were  recently  undertaken,  the  lack 
of  agreement  in  measuring  instruments  and  the  tendency  to 
rush  work  without  any  adequate  precautions  to  secure  an  exact 
agreement  of  temperature  between  the  test  samples  and  the 
standard  bridge  wire  were  the  cause  of  serious  discrepancies 
between  producers  of  copper  and  manufacturers,  or  consumers, 
of  wire.  Another  variation  resulted  from  the  practice  in  rolling 
mills  of  testing  hard-drawn  wire  and  calculating  the  resistance  by 
the  measurement  of  the  average  cross-section.  As  long  stretches 
of  wire  are  seldom  perfectly  round,  such  a  value  is  more  or  less 
inaccurate,  and  the  standard  specifications  of  the  American 
Society  for  Testing  Materials  now  provide  that  all  tests,  in 
case  of  disagreement  between  two  parties,  shall  be  made  on  wire 
of  .080  inch  diameter  by  the  meter-gram  system. 

Each  instrument  should  be  provided  with  a  set  of  extra  wires, 
whose  resistance  has  been  certified  by  a  national  Bureau  of 
Standards.  One  of  these  wires  may  then  be  placed  upon  the 
bridge  each  day  to  detect  any  change  in  the  instrument.  Wire 
samples  are  cleaned  and  straightened,  and  placed  within  the 
case  of  the  bridge.  Fifteen  minutes  ought  to  be  allowed  for 
the  samples  to  attain  the  temperature  of  the  closed  case,  after 
which  they  may  be  tested  at  the  rate  of  about  one  in  five  min- 


276  ANALYSIS    OF    COPPER 

utes  without  raising  the  temperature.  If  the  wire  is  touched 
with  the  bare  hands  in  making  the  connections,  the  resistance 
may  be  raised  as  much  as  .4  per  cent.  All  wires  should  be 
brightened,  if  necessary,  at  the  points  where  connections  are 
made  with  knife-edge  contacts,  by  rubbing  with  a  little  chamois 
skin  and  precipitated  chalk.  The  machine  standards,  etc.,  are 
cleaned  with  the  soft  skin,  only. 

R.  F.  Wood  1  has  devised  a  very  simple  straightener  for  short 
lengths  of  copper  wire.  It  consists  of  a  (36"  x  5"  x  1.5")  cast- 
iron  slab  faced  on  the  lower  side  with  a  smooth  hard-wood  board, 
one  inch  thick.  The  slab  is  fitted  with  two  straight  iron  handles 
on  the  edge  facing  the  operator,  and  the  wires  are  rolled  under 
this  weight  a  few  times  upon  a  second  smooth  board  which  rests 
on  a  small  work-table. 

The  electrical  conductivity  of  hard-drawn  copper  wire  is 
ordinarily  about  2.5  to  2.7  per  cent  lower  than  that  obtained  on 
the  same  samples  when  annealed.  It  is  a  well-known  fact  that 
this  difference  is  relative  and  variable  and  depends  first  on  the 
conditions  of  manufacture,  and  secondly  on  the  grade  of  the  cop- 
per, whether  it  is  high-grade,  or  extremely  arsenical.  As  the 
conductivity  of  copper  wire  is  reduced  by  the  presence  of  arsenic, 
etc.,  we  finally  reach  a  point  (which  according  to  the  author's 
experiments  lies  between  64.5  and  62.5  per  cent  conductivity) 
where  the  conductivity  of  the  hard-drawn  and  annealed  wire 
from  the  same  sample  have  the  same  value.  Below  this  con- 
ductivity, the  hard-drawn  wire  will  have  a  value  above  the 
annealed,  although  the  difference  increases  slowly.  Conductivity 
tests  of  64.5  per  cent  and  62.5  per  cent  correspond  to  .16  per 
cent  and  .18  per  cent  of  arsenic,  respectively. 

By  making  a  large  number  of  determinations  of  the  "  con- 
ductivity" of  samples  of  wire  (both  annealed  and  hard-drawn)  in 
which  the  arsenic  has  been  determined  (or  the  arsenic  and  anti- 
mony in  the  case  of  electrolytic  copper) ,  a  curve  of  reasonable  ac- 
curacy may  be  plotted  with  the  conductivities  as  ordinates  and 
the  percentages  of  arsenic  as  abscissae.  From  this  curve,  the  per- 
centage of  arsenic  may  be  quickly  taken  with  sufficient  accuracy 
for  many  purposes.  The  time  of  wire-drawing  and  testing  need 
not  exceed  one-half  hour  for  single  samples.  Such  a  chart, 
covering  a  range  from  103  per  cent  down  to  30  per  cent  con- 
1  Formerly  chemist,  Quincy  Smelting  Works. 


STANDARD   SPECIFICATIONS    FOR    COPPER  277 

ductivity,  has  been  prepare^  and  used  by  several  companies  for 
the  rapid  grading  of  refined^  copper.  Lawrence  Addicks  has 
plotted  charts  showing  the  effect  of  different  impurities  on  copper, 
but  the  determinations  were  made  on  crucible-melted  copper, 
which  is  practically  deoxidized  in  the  process.  The  values  ob- 
tained with  metal  remelted  in  crucibles  may  be  1  to  4  per  cent 
lower  than  the  conductivity  of  furnace-refined  copper  containing 
the  same  amount  of  the  special  impurity  in  question.  Refined 
metal  from  which  most  of  the  arsenic  has  been  removed  by  long 
rabbling  with  soda-lime  flux,  will  show  a  trifle  higher  conduc- 
tivity, than  untreated  copper  having  the  same  percentage  of 
arsenic. 

STANDARD  SPECIFICATIONS  FOR  COPPER 

The  following  paragraphs  summarize  the  chemical  and  elec- 
trical requirements  included  in  the  specifications  for  ordinary 
forms  of  "Lake"  and  "electrolytic"  cast  and  wrought  copper, 
which  were  adopted  August  25,  1913,  by  the  American  Society 
for  Testing  Materials,  and  have  been  reprinted  in  the  Year  Book 
for  1914. 

7.  Electrical    Requirements.  —  In    order    to    be    classed    as 
"Lake,"  the  copper  must  originate  on  the  northern  peninsula 
of  Michigan,  U.  S.  A.     Lake  copper  offered  for  electrical  pur- 
poses, whether  fire   or  electrolytically  refined,  is   termed  "Low 
Resistance    Lake."      Such    Lake    wire    bars,    or    "Electrolytic" 
wire   bars,  are   permitted   to   have   a  resistivity  not   to   exceed 
.15535  international  ohm  per  meter-gram  at  20°  C.  (as  shown  by 
test  on  annealed  wire).    All  ingots  and  ingot  bars  are  permitted 
to  have  a  resistivity  not  to  exceed  .15694  ohms  per  meter-gram 
at  20°  C.  (annealed).     Cakes,  slabs,  and  billets  come  under  the 
ingot  classification,  except  when  specified  for  electrical  use  when 
purchased,  which  would  bring  them  under  a  wire-bar  classification. 
Lake  copper  having  a  resistance  greater  than  .15694  int.  ohm 
per  meter-gram  at  20°  C.,   is  termed   "High  Resistance  Lake." 
Its  quality  is  due  to  arsenic,  without  other  foreign  elements. 

8.  Chemical     Requirements.  —  "Electrolytic"     copper    and 
"Low  Resistance  Lake"  copper  are  required  to  have  a  purity  of 
at  least  99.88  per  cent  as  determined  by  electrolytic  assay,  silver 
being  counted  as  copper.     "High  Resistance  Lake"  copper  is  re- 
quired to  have  a  purity  of  at  least  99.88  per  cent,  —  copper, 


278 


ANALYSIS    OF    COPPER 


silver,  and  arsenic  being  counted  together;  the  limiting  amount 
of  arsenic  being  a  subject  of  agreement  at  the  time  of  purchase. 
The  remaining  paragraphs  of  the  complete  specifications  deal 
with  the  physical  requirements,  allowable  errors  in  weights,  and 
variations  in  sizes  of  cast  copper  plates  or  wire,  and  finally  the 
manner  of  presentation,  investigation,  and  settlement  of  claims. 

INTERNATIONAL  ATOMIC  WEIGHTS  FOR  1916 


Element- 
Name  . 

Sym- 
bol 

Atomic 
Weight 

Loga- 
rithm 

Name  of  Element 

Sym- 
bol 

Atomic 
Weight 

Loga- 
rithm 

Aluminum 

Al 

27.1 

1.43297 

Molybdenum 

Mo 

96.0 

1.98227 

Antimony 

Sb 

120.2 

2.07990 

Neodymium 

Nd 

144.3 

2.15927 

Argon 

A 

39.88 

1.60075 

Neon 

Ne 

20.2 

1.30535 

Arsenic 

As 

74.96 

1.87483 

Nickel 

Ni 

58.68 

1.76849 

Barium 

Ba 

137.37 

2.13789 

Niton,  emana. 

Nt 

222.4 

2.34714 

Bismuth 

Bi 

208.0 

2.31806 

Nitrogen 

N 

14.01 

1.14644 

Boron 

B 

11.0 

1.04139 

Osmium 

Os 

190.9 

2.28081 

Bromine 

Br 

79.92 

1.90266 

Oxygen 

0 

16.0 

1.20412 

Cadmium 

Cd 

112.4 

2.05077 

Palladium 

Pd 

106.7 

2.02816 

Caesium 

Cs 

132.81 

2.12323 

Phosphorus 

P 

31.04 

1.49192 

Calcium 

Ca 

40.07 

1.60282 

Platinum 

Pt 

195.2 

2.29048 

Carbon 

C 

12.00 

1.07918 

Potassium 

K 

39.1 

1.59218 

Cerium 

Ce 

140.25 

2.14691 

Praseodymium 

Pr 

140.9 

2.14891 

Chlorine 

Cl 

35.46 

1.54974 

Radium 

Ra 

226.4 

2.35488 

Chromium 

Cr 

52.0 

1.71600 

Rhodium 

Rh 

102.9 

2.01242 

Cobalt 

Co 

58.97 

1.77063 

Rubidium 

Rb 

85.45 

1.93171 

Columbium 

Cb 

93.5 

1.97081 

Ruthenium 

Ru 

101.7 

2.00732 

Copper 

Cu 

63.57 

1.80325 

Samarium 

Sa 

150.4 

2.17725 

Dysprosium 

Dy 

162.5 

2.21085 

Scandium 

Sc 

44.1 

1.64444 

Erbium 

Er 

167.7 

2.22453 

Selenium 

Se 

79.2 

.  89873 

Europium 

Eu 

152.0 

2.18184 

Silicon 

Si 

28.3 

.45179 

Fluorine 

F 

19.0 

1.27875 

Silver 

Ag 

107.88 

.  03294 

Gadolinium 

Gd 

157.3 

2.19673 

Sodium 

Na 

23.0 

.36173 

Gallium 

Ga 

69.9 

1.84448 

Strontium 

Sr 

87.63 

.94265 

Germanium 

Ge 

72.5 

1.86034 

Sulphur 

S 

32.06 

.50596 

Glucinum 

Gl 

9.1 

0.95904 

Tantalum 

Ta 

181.5 

2.25888 

Gold 

Au 

197.2 

2.29491 

Tellurium 

Te 

127.5 

2.10551 

Helium 

He 

4.00 

0.60206 

Terbium 

Tb 

159.2 

2.20194 

Holmium 

Ho 

163.5 

2.21352 

Thallium 

Tl 

204.0 

2.30963 

Hydrogen 

H 

1.008 

.00346 

Thorium 

Th 

232.4 

2.36624 

Indium 

In 

114.8 

2.05994 

Thulium 

Tm 

168.5 

2.22660 

Iridium 

Ir 

193.1 

2.28578 

Tin 

Sn 

118,7 

2.07445 

Iodine 

I 

126.92 

2.10353 

Titanium 

Ti 

48.1 

1.68215 

Iron 

Fe 

'55.84 

1.74695 

Tungsten 

W 

184.0 

2.26482 

Krypton 

Kr 

82.92 

1.91866 

Uranium 

U 

238.2 

2.37694 

Lanthanum 

La 

139.0 

2.14301 

Vanadium 

V 

51.0 

1.70757 

Lead 

Pb 

207.2 

2.31597 

Xenon 

Xe 

130.2 

2.11461 

Lithium 

Li 

6.94 

0.84136 

Ytterbium 

Yb 

173.5 

2.23930 

Lutecium 

Lu 

175.0 

2.24304 

Yttrium 

Yt 

89.0 

1.94939 

Magnesium 

Mg 

24.32 

1.38596 

Zinc 

Zn 

65.37 

1.81538 

Manganese 

Mn 

54.93 

1.73981 

Zirconium 

Zr 

90.6 

1.95713 

Mercury 

Hg 

200.6 

2.30233 

CHEMICAL    CONVERSION    TABLE 


279 


CHEMICAL  CONVERSION  TABLE 


Elements 

•*•  Compounds 
Weighed 

Required 

Factors 

Loga- 
rithms 

Aluminum 

A12O3 

Al 

53033 

-1  72455 

A1PO4 

Al 

22188 

-1  34612 

A1PO4 

A12O3 

41837 

-1  62156 

Arsenic  

3  Ag 

As 

23162 

-1  36478 

As2O3 

As 

75748 

-1  87937 

As2S3 

As 

60918 

-1  78475 

Mg2As2O7  

As  

.  48274 

-1.68372 

Mg2As2O7  
Mg2As2Oy 

As2O3  

As2S3 

.63730 
79244 

-1.80434 
-1  89897 

Antimony 

Sb2O4 

Sb 

78975 

-1  89749 

Sb2S3 

Sb 

71424 

-1  85384 

Sb.   . 

Sb2O5 

1  33280 

0  12477 

Barium  

BaCO3 

Ba 

69600 

-1  84261 

BaCO3     . 

BaO 

77707 

-1  89046 

BaCrO4 

Ba 

54217 

-1  73414 

_, 

BaCrO4 

BaO 

60532 

-1  78198 

BaSO4  .... 

Ba 

58848 

-1  76973 

BaSO4.  . 

BaO 

65702 

-1  81758 

BaSO4 

BaCO3 

84552 

-1  92712 

Bismuth  

Bi2O3 

Bi 

89656 

-1  95258 

BiOCl 

Bi 

.  80166 

-1  90399 

Bi2S3  .. 

Bi 

.81221 

-1  90972 

Bromine  

AgBr  

Br 

.  42556 

-1  62896 

Cadmium  

Cj 
Q  .  .  .  . 

CdO 

1  .  14235 

0  05780 

CdS  

Cd 

.  77807 

-1  89103 

CdSO4  .  .  . 

Cd 

.  53919 

-1  73174 

Cd2P2O7     . 

Cd 

.  56358 

-1  75096 

Calcium  

CaSO4  

CaO 

.41188 

-1  61477 

CaO  

CaCO3 

1  .  78473 

0  25157 

CaSO4  
CaO  

CaF2  
CaF2 

.  57350 
1  .  39237 

-1.75853 
0  14375 

(tit  ration) 

Na2C2O4  

CaO.  . 

.  41843 

-1.62162 

Carbon  

BaCO3  
BaCO3  

C  
CO2.. 

.  06080 
.  22293 

-1.78390 
-1.34817 

• 

CO2 

C 

27273 

-1  43573 

Chlorine 

AgCl 

Cl 

24738 

-1  39336 

NaCl  

Cl.. 

.  60657 

-1  .  78288 

Chromium 

BaCrO4 

Cr 

20523 

-1  31224 

BaCrO4  
BaCrO4  
Cr2O3 

Cr203.... 
Cr03  
Cr 

.29996 
.39468 
68421 

-1.47706 
-1.59625 
-1  83519 

PbCrO4 

Cr 

.16089 

-1  20653 

Cobalt  

PbCrO4  
PbCrO4  
CoO. 

Cr203.... 
Cr03  
Co 

.23515 
.  30941 

.  78658 

-1.37135 
-1.49053 
-1  89574 

Copper 

Co  
CoSO4  
Cu2S 

CoO  
Co  
Cu 

1.27132 
.  38038 
79862 

0.  10425 
-1.58022 
-1  90234 

Cu  
Cu  
Cu2(SCN)2  
CuSO4(5H2O)  

CuO  
Cu2O  
Cu  
Cu  

1.25169 
1.12585 
.52260 
.  25457 

0.09750 
0.05148 
-1.71817 
-1.40581 

280  ANALYSIS   OF   COPPER 

CHEMICAL  CONVERSION  TABLE  —  Continued 


Elements 

Compounds 
Weighed 

Required 

Factors 

Loga- 
rithms 

Fluorine  

CaF2 

F 

48674 

-1  68730 

CaSO4 

F2 

27914 

-1  44582 

CaO 

CaF2 

1  39236 

0  14375 

Hydrogen  .  .   .  . 

H2O 

H 

11190 

-1  04883 

Iodine  ... 

Agl 

I 

54055 

-1  73284 

KI 

I 

76449 

-1  88337 

Iron  

Fe2O3 

Fe 

69940 

-1  84473 

Fe 

FeO 

1  28653 

0  10942 

FeO  

Fe2O3  .... 

1.11136 

0.04586 

Fe2O3 

Fe3O4 

96660 

-1  98525 

Lead 

PbSO4 

Pb 

68324 

-    83457 

(electrolysis) 

PbO2(210-230°C.)  . 

Ph.. 

.  86430 

-  .93667 

PbO2  (theory)  
PbCrO4  

Pb  
Pb  

.86622 
.  64109 

-  .93763 
-  .80692 

PbO2  

Pbs  ? 

1.00025 

.00011 

Magnesium 

Mg2P2O7 

Me 

21843 

-    33931 

Mg2P2O7  

MgO  

.36213 

-  .55886 

Manganese 

MnO2 

Mn 

63189 

-    80064 

Mn2P2O7  

MnO2  .  . 

.61231 

-  .78697 

Mn2P2O7  

MnO    . 

.49961 

-1  .  69863 

Mn2P2O7    .  .    . 

Mn  . 

.  38691 

-1  .  58761 

Nickel  

Ni     . 

Nio 

1.27267 

0  10472 

Phosphorus  

Ni(C8H1404N4)  .... 
Am.  Phos.  Molyb.. 
Mg2P2O7  

Ni  
P  
P  

.  20316 
.01630 

.  27874 

-1.30784 
-2.21219 
-1.44520 

Platinum    . 

Mg2P207  
K2PtCl6 

P205  
Pt 

.63793 
40151 

-1.80477 
-1  60370 

Potassium    . 

K2PtCl6 

K2O 

19376 

-     28726 

Pt  

K2O  

.  48258 

-  .68357 

K2Pt2Cl6.. 

KC1  

.  30673 

-1.48676 

Silicon 

SiO2 

Si 

46932 

-     67147 

SiO2  

SiO3  

1  .  26534 

0.  10221 

Silver 

AgBr 

Ae 

57444 

-     75924 

AgCL. 

Ag.. 

.  75262 

-  .87658 

Sodium  

Agl  
AgCl  

A 

Ag  
NaCl  

.  45945 
.40784 

-  .66223 
-  .61049 

AgCl  
NaCl  

Na2O.... 
Na2O 

.43254 
.  53028 

-  .63603 
-1.73451 

Sulphur  

BaSO4  

S  .    .      . 

.  13735 

-1.13778 

Tellurium  

BaSO4  
Te     

S03  
TeO2 

.34297 
1  25098 

-1.53526 
0  09725 

Tin  

SnO2    .  .  . 

Sn 

78766 

-1  89634 

Sn     . 

SnO2 

1  26959 

0  10366 

Tungsten  

WO2     . 

W 

85185 

-1  93036 

WO3 

w 

79310 

-1  89933 

Zinc 

ZnS 

Zn 

67094 

-1  82668 

ZnO  
Zn2P2O7  

Zn  
Zn  

.  80337 
.42891 

-1.90492 
-1.63237 

INDEX 


Accessories  for  assay  furnaces,  240 
Acetate  of  ammonium,  reagent,  40 
Acid,  hydrochloric,  normal  solution, 

42 

mixture  for  electrolytic  assay,  49 
refinery  electrolyte,  154 
quality,  c.  p.  hydrochloric,  37 
quality,  nitric  and  sulphuric,  38 
sulphuric,  normal  solution,  49 
Alloys — see  brass,  bronze,  monel,  etc. 

Carbon  combustion,  251 
manganese  determination,  244 
nickel,  analysis,  245 
sulphur,  246 
zinc  estimation,  247 
Aliquoting    apparatus,    general    de- 
scription, 4 

manipulation,  copper  assay,  172 
Alumina,  in  ores  and  slags,  73 
Aluminum,    in    chrome   refractories, 

123 

in  metallic  copper,  225 
refinery  electrolytes,  158 
Ammonium  acetate,  reagent,  40 
ferric  sulphate,  reagent,  42 
ferrous,   sulphate,   standard  so- 
lution, 47 

hydroxide,  purity,  38 
molybdate,   standard   and  indi- 
cator, 40 

oxalate,  precipitant,  40 
phosphate,  precipitant,  40 
sulphydrate,  reagent,  41 
thiocyanate,   reagent   and  stan- 
dard solution,  41 

Anodes,  electrolytic  assay,  172-176 
gold  and  silver,  163-169 
sampling,  25 


Anode  slags,  sampling  (for  assay  see 
"slags"),  24 

slimes,  arsenic,  gold  and  silver,  160 
insoluble,  lead  and  copper, 

161 

cobalt  and  nickel,  162 
sulphur,     platinum,  %  palla- 
dium, insoluble,  163 
Antimony  in  anodes,  rapid  electro- 
lytic separation,  196 

crude    copper,   separation    from 
tin  and  arsenic,  194 

refined    copper,    basic    method 
with  ferric  hydroxide,  200 

copper,  combination  method,  in- 
cluding Se  and  Te,  205 

copper,    final    separation    after 
arsenic,  210 

separation  from  tin,  basic  meth- 
ods, 211 

ores,  by  fusion  and  titration,  86 

ores,  by  electrolysis,  87 

ores  and  slags,  separation  from 
tin,  88 

refinery  electrolytes,  158 

silver  slimes,  162 

Apparatus  for  electrolysis  of  copper, 
description,  6-10 

aliquoting  of  solutions,  4 

circulation  of  electrolytes,  11 

distillation  of  arsenious  chloride, 
203 

oxygen  in  copper,  229 

polishing    metals    for    photomi- 
crographs, 252 

photography  of  metal  sections, 
255 

resistivity   of   copper   wire,    de- 
scription, 275 

sampling  of  mill  tailings,  19 


282 


INDEX 


Arsenic  in  anodes,  rapid  electrolytic 
separation,    western    method, 
196 
Mansfeld  copper,  198 

separations,      formula     for 

electrolytic,  199 

refined  copper,  separation  with 
ferric  hydroxide,  200 

distillation  with  hypophos- 

phorous  acid,  202 
distillation  with  ferrous  salt, 

203 
treatment  of   distillate,  by 

•  titration,  204 
precipitation    by    hydrogen 

sulphide,  204 

copper,  alkaline  method,  includ- 
ing antimony,  selenium  and 
tellurium,  205 

separation    from    antimony 

and  tin,  207 
precipitation    by    magnesia 

mixture,  208 

ores,  distillation  method,  83 
slags,  distillation,  84 
ores  and  slags,  by  fusion  and  di- 
gestion with  acid,  85 
ores  and  slags,  by  sintering,  84 
ores  and  slags,  traces,  evolution 

as  arsine,  84 
ores  and  slags,  separation  from 

tin,  88 

refinery  electrolytes,  159 
silver  slimes,  160 

Arsenite   of  sodium,    titrating   solu- 
tion, 48 
Assaying,  copper  in  ores  and  slags, 

51-64 

native  copper  ore,  138 
gold    and    silver    in    ores    and 
mattes,    commercial    require- 
ments, 125 
gold  and  silver,  crucible  method 

for  ores,  etc.,  126 
gold   and   silver,    eastern   assay 

with  excess  litharge,  129 
gold  and  silver,  western  method, 
soda-niter,  130 


Assaying,'  mattes  by  scorification,  132 
lead    in    ores,    and    slags,    acid 

methods,  93 

lead  in  ores,  fire  assay,  126 
Assay  weights,  explanation  of  "assay 

ton"  system,  125 
Atomic  weights  for  1916,  278 

B 

Barium  chloride,  solution,  42 

hydroxide,  reagent  and  solution, 

41 

in  residue  of  ores  and  slags,  70 
in  presence  of  lead,  89 
Bichromate  of  potassium,   standard 

solution,  46 
Bismuth,  in  ores  and  slags,  technical 

assay,  88    „ 

in  ores  and  slags,  accurate  analy- 
sis, 89 
metallic  copper   as  oxychloride, 

214 
metallic      copper,      colorimetric 

assay,  215 

sulphate,  standard  solution,  42 
Blast  furnace  slags  —  see  slags 
Blister  —  see  converter  and  anodes 
Boron  in  metallic  copper,  225 
Brass,    copper,    technical    assay    (in 

absence  of  tin),  236 
copper  in  leaded  brass  (with  tin), 

239 
iron   in   presence   of   tin,    exact 

method,  240 

lead  by  "lead  acid,"  238 
lead  by  electrolysis,  technical,  239 
lead,  exact  methods,  239-240 
manganese,  244 
sulphur,  determination,  246 
tin  in  leaded  alloy,  237 
zinc,  237,  in  presence  of  tin,  239 
Bromide  of  potassium,  silver  precipi- 
tant, 172 
Bromine,  reagent,  calcium,  77 

manganese  determination,  217 
separation  Mn  and  zinc,  117 
Bronzes     (tin-iron     alloys),     copper 
assay,  two  methods,  241 


INDEX 


283 


Bronzes,    iron    and    tin,   aqua-regja 

method,  242 
carbon  by  combustion,  in  nick- 

eliferous  alloy,  2#1 
lead,  small  amounts,  242 
manganese,  244 
phosphorus,  by  titration,  243 
tin  with  iron,  242 
zinc,  determination,  247 
Bullion,   sampling   at   refineries   and 

custom  works,  25 
assaying,    copper   in   slabs   and 

anodes,  165 
cupellation,  unparted  basemetal, 

143 

silver  with  antimony,  143 
silver,   with  bismuth,    selenium, 

and  tellurium,  144 
fine  gold  and  silver,  cupellation, 

Mint,  145 

containing  platinum,  146 
fusion  with  cadmium  and  titra- 
tion (auriferousj,  153 
sampling  at  Mints,  33 
sampling  at  refineries,  34 
silver,   humid    assay    by    Mint, 

148 
silver,    titration    with    thiocya- 

nate,  152 

C 

Cabinets,  for  electrolysis,  6-10 
Cadmium,  assay  in,  ores,  separation 

from  copper,  90 
ores,  separation  from  zinc,  119 
zinc  spelter  (as  sulphate),  256 
zinc  spelter  (by  electrolysis),  257 
zinc    (separation    by    trichlora- 

cetic),  258 

Cadmium  chloride,  reagent  for  sul- 
phur, 42 

Calcium  determination,  clays,  121 
chromite  and  refractories,  122 
ores  and  slags,  western  oxalic 

method,  77 

ores  and  chilled  cupola  slags,  77 
reverberatory    slags,     and    flue 
dust,  78 


Calcines,  see  determinations  in  ores 
Calculations,     accuracy     of     copper 

analysis,  1 

tables  of  chemical  factors,  279 
Carbon  monoxide  and  dioxide,  prep- 
aration, 38 
dioxide  in  oxygen  determination, 

226 

Carbon,  copper-nickel  alloys,  by  com- 
bustion, 251 
Casting   small   metal   specimens  for 

microscope,  268 

Chemical  conversion  tables,  279 
Chemically  pure  acids,  quality,  37 
Chlorides  in  refinery  electrolyte,  157 
Chlorides  in  slimes,  note,  161 
Chloride  of  copper,  solution,  42 
Chromium,    volumetric,     90;     com- 
pounds, complete  analysis,  122 
Circulation  by  Frary  device,  11 
Citrate  of  sodium,  reagent  in  titra- 
tion, 48 

Classification,  slags  and  ores  by  solu- 
bility, 69 

subject  matter  of  book,  1 
Clays,  complete  analysis,  121 
Coal,  sampling  of  cargoes  at  smelter, 

30 

reduction  to  assay  sample,  32 
Cobalt,   ores  and  furnace  products, 

electrolysis,  103 
Mansfeld  ores,  ether  separation, 

104 

separation  from  little  nickel,  106 

separation  from  much  nickel,  107 

from  nickel  and  zinc  in  copper, 

choice  of  method,  218 
in  copper,  by  electrolysis,  220 
refinery  electrolytes,  158 
silver  slimes,  162 
Conductivity  of  copper  wire,  272 
Conversion  tables,  279 
COPPER  IN  ALLOYS  —  Brass,  with  or 

without  tin,  236 
bronzes,  electrolysis,  241 
nickel  alloys,  monel  metal,  248 
refined  nickel,  253 
zinc  spelter,  with  cadmium,  256 


284 


INDEX 


COPPER  ASSAYING: 

Mattes,  eastern  method,  64 
Ores,  by  titration  with  iodide,  51 
titration  with  cyanide,  53 
thiocyanate  and  permanga- 
|    nate,  54 
colorimetric  assay,  western, 

55 
colorimetric,    permanent 

standards,  57 
colorimetric,       Mansfeld 

shales,  58 
electrolytic  assay,  limits  of 

accuracy,  59 
electrolytic,   slags,  western, 

60 

electrolytic,  chilled  slags,  ^61 
raw  ores,  eastern  method  of 

electrolysis,  62 
calcines  and  cinders,  eastern 

method,  64 
Mansfeld  ores,    electrolysis, 

64 

Slags,  Mansfeld  slags  and  resi- 
dues, 66 

Mansfeld      typolite      slags,  . 
magnetic  separation,  66    X 
native  copper,  concentrates, 

fire  assay,  138 

Refinery  electrolytes,   by  titra- 
tion with  cyanide,  155 

electrolysis,  157 
Silver  refinery  slags,  164 
Silver  slimes,  161 
COPPER  METAL  —  Valuation: 

Crude   copper,    converter,  slabs 
and    anodes,    preparation    of 
samples,  172,  electrolysis,  176 
assay  in  presence   of    sele- 
nium or  tellurium,  180 
foreign  metals,  notes,  182 
gold  and  silver,  fire  assay,  166 
gold  and  silver,  wet  assay, 

167 

moisture  in  castings,  29 
low-grade,  nickelif erous 
products    (leady  mattes), 
179 


Refined  copper,  electrolytic  ten- 
gram  assay,  183 

standard  five-gram  assay,  184 
rapid    assay,    rotary,    so)e- 
noid,  189 

Casting  brands,  electrolysis,  187 
COPPER  ANALYSIS  —  aluminum,  225 

anodes,    arsenic   and   antimony ,- 
electrolysis,  196 

antimony  and  arsenic,  Mansfeld 
method,  198 

antimony,  electrolytic  separation 
from  arsenic  and  tin,  199 

antimony,  exact  separation,  211 

arsenic,  distillation,  202-203 

arsenic,    as   sulphide,   from  dis- 
tillate, 204 

arsenic,    by   magnesia   mixture, 
208 

arsenic,  antimony  and  tin,  exact 
separation,  basic,  200 

arsenic  group  with  selenium  and 
tellurium,  alkaline  method,  205 

arsenious     acid,     titration     by 
iodine,  204 

bismuth,  as  oxychloride,  214 

bismuth,  colorimetric,  215 

boron,  with  qualitative  test,  225 

cobalt,    from    nickel    and    zinc, 
organic  reagent,  218 
electrolysis,  220 

lead,  electrolysis,  221 

manganese,  216 

oxygen  and  occluded  gases,  226 

phosphorus  (see  also  alloys,  243), 
225 

sulphur,  exact  analysis,  224 

tin,  from  arsenic  and  antimony, 
basic,  211-214 

tin,  electrolytic  separation,  crude 
metal,  194-199 

tin    in    remelted    copper,    from 
scrap,  232 

zinc,  from  cobalt  and  nickel,  218 
Copper   flasks,    for   aliquoting   solu- 
tions, 4 

Copper-potassium  chloride,  reagent, 
42 


INDEX 


285 


Copper  specifications,  classifications, 
277 

Crystallography  of  coppet  and  alloys, 
259 

Current  density,  standard,  5 

Cyanide  of  potassium,  standard  solu- 
tions, 45 

D 

Data — electrical  power  and  current,  5 
Density  vs.  specific  gravity,  defini- 
tion, 37 

Density  of  copper,  273 
Dimethyl  glyoxime,  reagent,  44 
Dore  (unparted  base  bullion) : 
cupellation  (antimonial),  143 
cupellation  (impurities  bismuth, 

selenium,  tellurium),  144 
silver  b.,  humid  assay,  148,  with 

platinum,  146 
silver,  thiocyanate,  152 
fusion    with    cadmium   (aurifer- 
ous), 153 
Drilling  machines,  sampling,  12 


Electrical    conductivity    of     copper, 

apparatus,  272,  formulas,  273, 

method,  274 
*  data  on  power,  5 
Electrolytic    assay,    copper   in   ores, 

limits,  59 

copper,  western  methods,  60 
copper  in  chilled  slags,  61 
ores,  and  cinders,  eastern  method, 

62-64 

Mansfeld  ores,  slags,  64-65 
crude  copper  metal,  apparatus, 

172,  assay,  176 

copper  (high-grade)  refined,  183 
casting  copper,  187 
Electrolytes,  copper  refinery: 
arsenic  by  distillation,  159 
antimony  from  copper,  158 
aluminum  and  cobalt,  158 
chlorine,  estimation,  157 
copper,  electrolysis,  157 
copper,  titration,  156 


Electrolytes,  nickel  and  zinc,  158-159 
sulphuric  acid,  titration,  153 

Electrolytic  slimes  —  see  slimes 

Etching-copper,  263 
aUoys,  264 


Factors,  tables,  279 
Ferric-ammonium  sulphate,  reagent, 

42 

Ferrous-ammonium  sulphate,  stand- 
ard solution,  47 
Ferro-cyanide  of  potassium,  titrating 

solution,  45 

Fire    assaying,    commercial   require- 
ments, 125  '"» 

copper,  native  concentrates,  138 
bullion,  for  gold  and  silver,  143 
ores  and  slags,  lead,  gold,  silver, 

platinum,  126 
Fire  clay,  analysis,  121 
Flasks  for  assay  of  crude  copper,  4 
Fluorine,  in  ores  and  slags,  91 
Flue  dust — see  copper  assay,  and  ore 

analysis 

Frary  rotary  device,  or  solenoid,  11 
Furnaces  for  assaying,  2 
Furnace  accessories,  3 

refractories,  analysis,  121 

G 

Gases,  preparation  of  carbon  monox- 
ide and  dioxide,  38 
hydrogen,  oxygen,  sulphur  diox- 
ide, 39 

German  silver,  carbon,  251 
copper,  electrolysis,  248 
nickel,  251 
'  sulphur,  246 

zinc,  248,  alternative,  249 
Glass-ware,  solubility,  71-117 
Glyoxime-dimethyl,  reagent,  44 
GOLD- ASSAY: 

Bullion,  cupellation  of  low- 
grade,  133 

cupellation  of  fine  gold,  144 
fusion  with  cadmium,  aurif- 
erous silver,  153 


286 


INDEX 


GOLD- ASSAY  (continued): 

crude     copper,     slabs    and 

anodes,  fire  assay,  166 
crude  copper,  mercury-sul- 
phuric acid  processr  167 
crude     copper,     bisulphate 

method,  169 
ores  and  furnace  products, 

crucible  assay,  126 
ores,  etc.,  soda-niter  western 

assay,  130 
ores    and    mattes,    eastern 

excess-litharge  assay,  129 
mattes,    scorification,    131, 

eastern  method,  132 
mattes,    combination    wet  .and 
fire  assay,  133,  low-grade  cop- 
per, 134 

rich  ores  and  mattes,  bisul- 
phate method,  134 
preparation    of    pure   gold, 

144 
sampling   at   Mints,   37,  at 

furnaces,  34 
separation  from  silver  and 

platinum,  135 
separation    from    platinum 

and  palladium  (indirect), 

137 
slags,    electrolytic   refinery, 

164 
slimes,  with  silver,  160 

H 

Hardness  of  etched  copper  and  alloys, 

268 
Hydrochloric  acid,   normal  solution, 

42 

reagent,  quality,  40 
Hydrogen,  preparation,  39 
Hyposulphites  —  see  thiosulphates. 


Insoluble  matter  in  —  raw  ores,  9 
roasted  ores,  calcines,  70 
ores  containing  barium  sulphate, 

70 
low-grade  bars,  leady  mattes,  179 


Insoluble   matter    in  —  nickeliferous 

copper,  180 
silver    slimes,     including      lead 

sulphate,  161 

silver  slimes,  lead  removed,  163 
Introduction,    classification    of    sub- 
jects, 1 

Iodide  of  potassium,  titrating  solu- 
tion, 46 

Iodide  method,  copper  titration,  51 
Iodine,  standard  solutions,  for  sulphur 

or  arsenic  titration,  43 
Iridium — see  platinum  135,  also,  137 
Iron,  in  brasses,  240 

bronzes  (alloys  with  tin  and  iron), 

242 

commercial  copper,  216 
from  drill  in  sampling  metal,  29 
from  grinding  plates,  18 
from  refinery  electrolytes,  158 
German  silver,  Monel  metal,  251 
nickel,  refined  metal,  253 
zinc  spelter,  255 

J-K 

Jena  glass,  solubility,  71-117 

L 
Lead  —  in  brass,  technical  assay,  238, 

exact  determination,  239 
composition  of  "lead  acid,"  238 
copper,  221,  check  assay,  223,  as 

metallic  lead,  223 
bronze,     separation     of     small 

amount,  242 
calcareous      ores,      chromate 

method,  95 
ores  and  mattes,  by  electrolysis, 

93,  rapid  assay,  94 
ores  and  mattes,  as  sulphate,  also 

tailings,  93 

zinc  spelter,   standard  methods, 
254 

special  titration,  257 
Literature  of  metallography,  270 
sampling,  36 

M 

Machine  for  metal  polishing,  262 


INDEX 


287 


Magnesium  chloride,  precipitant,  44 
clays  and  sands,  determination, 

121 
chilled  cupola  slags,  77 

chromite  and  refractories,  122 
reverberatory     slags     and     flue 

dust,  78 
sulphate,  43 

Magnetic  treatment,  typolite  slags,  66 
Manganese  in  copper,  determination, 

216 

alloys,  244 
rich  ores,  also  iron  or  steel,  bis- 

muthate,  97 
ores  and  slags,  Volhard  method, 

96 

sulphate,  reagent,  solution,  43 
Mansfeld  ores,  assaying,  66 
Mattes,    copper  assay,   titration  by 

iodide,     51,     cyanide,      53, 

thiocyanate,   54 
special  eastern  method,  64 
gold  assay,  crucible,  soda-niter, 

130 
gold,   scorification,   131,   eastern 

method,  132 
leady  mattes,  special  assay  for 

gold  and  silver,  134 
nickel,  titration,  101 
sampling,     eastern     works,     22, 

western,  24 

silver,  gold  and  platinum,  sepa- 
ration, 135 

Mechanical  sampling,  17-22 
Metal     specimens,     preservation    of 

etched  surface,  268 
Metallography,     apparatus,     micro- 
scope and  accessories,  265 
casting  of  small  specimens,  268 
crystallography,  259 
definition  and  purposes,  259 
etching  of  brass  and  bronze,  264 
etching  of  copper,  263 
hardness  of  etched  surfaces,  268 
photography,  manipulation,  266 
photomicrographs,  plates,  269 
polishing    and    selection    of 

samples,  261 


Metallography,  preservation  of  etched 

specimens,  268 
nomenclature,  269 
references  to  literature,  270 
Methods,  accuracy  required,  1 
Mines,  sampling  and  valuation,  14 
Mixture    of    acids    for    electrolytic 

assay,  40 
Moisture  samples  —  coal,  mines,  30, 

reduction  in  laboratory,  32 
ore  and  mattes,  23 
castings  of  crude  copper,  correc- 
tion, 29 
Molybdate  of  ammonium,  solution, 

40,  Molybdenum,  note,  99 
Monel  metal,  carbon,  nickel  determi- 
nation, 251 

copper,  electrolysis,  248 
sulphur,  246 
zinc,  248 

N 

Native  copper  —  fire  assay,  138 
Normal  current  density,  5 
Nickel  alloys,  analysis,  copper,  248 

carbon,  251 

nickel  in  small  amounts,  245 

nickel  in  large  percentages,  248 

sulphur,  246 

zinc,  248 
Nickel  in  copper  metal,  218-220 

mattes,  titration,  101 

ores,  separation  from  cobalt,  106 

ores,  electrolysis,  103 

ores  and  slags,  ether  separation, 
104 

refinery  electrolytes,  158 

silver  slimes,  162 

Nickel    metal,    refined,    electrolytic 
assay,  252 

copper  and  iron,  253 
Nitrose-beta-naphthol,  precipitant,  44 

O 

Office,  records,  1 

Ores  of  copper,  assaying,  for  copper, 

103 
colorimetric  assay,  56 


288 


INDEX 


Ores  of  copper,  cyanide  titration,  53 

iodide,  51 

thiocyanate,  54 

electrolysis,  60 

Mansfeld  ores,  color  and  elect.,  58 
typolite  ore  (and  slags),  64 

gold  and  silver,  Aaron's  method, 
126 

gold  and  silver,  soda-niter,  130 

gold  and  silver,  excess  litharge, 
129 

same,  rich  ores,  bisulphate,  134 

lead,  fire  assay,  western,  126 

lead,  wet  assay,  93  —  calcareous 
ores,  jchromate,  95 

platinum,  palladium,  135-137 
Ore  analysis  —  alumina,  73 

antimony  and  arsenic,  fusion  and 
digestion,  85 

antimony,  electrolysis,  87 

antimony,   arsenic,   tin,   separa- 
tions, 88 

arsenic,  distillation,  83 

barium,  in  silica,  as  sulphate,  70 

barium,  direct  assay,  89 

bismuth,  technical  assay,  88 

bismuth  accurate  method,  89 

calcium,  78 

cobalt  (with  nickel),  103 

fluorine,  91 

insoluble,  raw,  69,  calcines,  70 

iron,  oxides,  74 

lead — see    ore  assaying  —  man- 
ganese, 96 

nickel,    electrolysis,    103,    ether 
method,  104 

potassium,  lithium,  sodium,  sepa- 
ration, 109 

potassium,  etc.,  indirect  separa- 
tion, 110 

potassium  and  sodium,  sintering 
method,  111 

sulphur,  79 

sulphur  in  zincy  or  leady  ores,  80 

sulphur      in      pyrites,      eastern 
methods,  81 

selenium  and  tellurium,  author's 
method,  111 


Ore     analysis  —  selenium    and    tel- 
lurium, Keller's  method,  112 
silica,  72 

tin,  separation,  88 
tin,  volumetric,  114 
zinc,    western    assay,    including 

mattes,  116 
zinc,  exact  method  of  Waring, 

118 

zinc,  Mansfeld  method,  120 
'Osmium,   with  platinum  and  palla- 
dium or  gold,  135 
same,  indirect  separation,  137 
Oxalate  of  ammonium,  reagent,  40 
Oxygen,  preparation,  39 

in  metallic  copper,  ignition,  226 
by  photomicrographs, 
(notes,  268),  231 


Palladium  —  see  platinum  below 
Permanganate  of  potassium,  calcium 

titration,  47 
iron  titration,  46 
Phosphate  of  ammonium,  precipitant, 

40 

Phosphate  of  sodium,  precipitant,  49 
Phosphorus,    in    copper,    determina- 
tion, 225 

in  alloys,  bronzes,  243 
in    ores    and    cinders,    same 

methods  modified,  225-243 
Photography  —  see  metalld|graphy 
for  copper  and  alloys,  manipula- 
tion, 265- 
index    to    plates,    copper    and 

alloys,  266 

photomicrographs,  267 
Platinum,   assay  in  ores,   slags  and 

matte,  western,  128 
direct  separation  from  gold  and 

silver,  135 
indirect     separation,     including 

palladium,  136 
with  gold  and  silver,  bisulphate 

method,  134 

with  palladium,  separation  from 
gold  and  silver,  135 


INDEX 


289 


Platinum,  silver  slimes  (with  palla- 
dium), 163  3 

from  anode  in  electrolytic  ass#y, 

187 
Polishing  of  specimens  for  etching, 

261 

Potassium  bromide,   precipitant  for 
silver,  172 

chromate,  solution,  46 

copper  chloride,  reagent  for  car- 
bon, 42 

Potassium    cyanide,    standard    solu- 
tions, 45 

ferro-cyanide,  standard  solution, 
45 

hydroxide,  normal  solution,  46 

iodide,  reagent  and  solution,  46 

permanganate,  for  iron  titration, 
46 

permanganate  for   calcium   and 
Mn,  47 

slags    and    ores,    determination, 
108 

separation  from  sodium  and  lith- 
ium, 109 

indirect,    tJy    calculation,    from 
chlorine,  110 

sintering  method  of  J.  L.  Smith, 
111 

thiocyanate,  precipitant,  47 
Power,  data  on  electric  currents,  5 
Pyrites,  sulphur  determination,  80-81 


Reagents — see  various  chemicals,  37 

Records,  office  systems,  1 

Refined  copper  —  see  copper  assaying, 

copper  analysis,  1 
standard  trade  specifications,  277 
Refractories,   chromium,  volumetric, 

90 

chromium  compounds,  brick,  ce- 
ment, 122 
clays,  sands,  complete  analysis, 

121 
Resistivity     of     copper,     apparatus, 

bridges,  272 
definitions,  U.  S.  standards,  273 


Resistivity  of  copper,  formulas,  cal- 
culations, 274 

methods  of  testing,  275 
Reverberatory  slags,  sampling,  23 

analyses,  see  slags,  73  etc. 

silica,  72 


Sampling,  anodes,  25,  Reduction  for 

assay  (also  165),  27 
bullion,  gold  and  silver,  Mints, 

33 

bullion,  refineries,  34 
coal,    cargoes,   30,  reduction    in 

office,  32 

correction,  iron  from  grinders,  18 
correction,  steel  from  drills,  29 
concentrates  at  smelters,  native, 

21 

concentrates,  at  mills,  mechani- 
cal, 18 

copper,  molten,  at  furnaces,  24 
copper,  bars,  cakes,  ingots,  30 
containers  for  coal  samples,  27 
crude  copper,  additional  notes, 

165 

literature,  references,  36 
'machine  design,  22 
mattes,    western    works,    24 

eastern  methods,  22 
mines,  valuation,  14 
mines,  practical  notes,  15 
moisture  sample  ores,  23 
ores,  eastern  custom,  hand  sort- 
ing, 21 

ores,  eastern  practice,  mechani- 
cal, machine  design,  22 
ores,  western  hand  work,  16 
ores,  western  mechanical,  17 
ore  sample  for  moisture,  23 
slags,  cupola  furnaces  (blast),  24 
slags,  reverberatory,  23 
tailings,  western,  17 
tailings,  native,  mechanical,  18 
zinc  spelter,  34 

Samples,    selection    for    photomicro- 
graphs, treatment,  261 
Sands,  furnace  linings,  analysis,  121 


290 


INDEX 


Segregation,   crude  copper,  26,  gold 

and  silver  bullion,  32 
Selenium  (and  tellurium)  in  copper, 

author's  method,  205 
in  copper,  Keller's  method,  233 
in  ores  and  slags,  111-112 
Silica  —  clays  and  sands,  121 
chromite  and  brick,  122 
in  ores,  72 

cupola  (blast  fur.)  slags,  70 
cupola  slags,  native  copper,  71 
reverberatory  slags  and  flue  dust, 

72 

Silver  assay,  anodes,  converter,  slabs, 

fire  assay,  166,  combination,  169 

anodes,    refined,    cupellation    of 

chloride,  171 

base  unparted  bullion,  cupella- 
tion, 143 
bullion,    fine,    Mint    assay,    by 

cupellation,  144 
bullion,    humid    assay    of    the 

Mints,  148 
bullion,     thiocyanate     titration, 

152 
bullion     (auriferous),     cadmium 

fusion,  153 

nitrate,  standard  solutions,  48 
ores,  slags  and  mattes,  Aaron's 
crucible  method,  126 

western  soda-niter  method, 

130 
excess  litharge,   eastern 

method,  129 

sodium  peroxide  fusion,  131 
rich  ores  and  mattes,  bisulphate 

method,  134 
scorification,   mattes    (low-grade 

ores),  132 

separation  from  gold  and  plati- 
num (or  palladium),  135 
separation,    indirect    method  of 

Dewey,  137 

slags  from  silver  refinery,  164 
slimes,  refinery,  160 
Slags,  analysis,  alumina,  73, 
arsenic,  83 
antimony,  electrolysis,  87 


Slags,   antimony  and  arsenic,  fusion 
method,  86 

barium  and  calcium,  77 

bismuth  (see  ores),  88-89 

copper,  as  in  ores,  51-64 

fluorine,  91 

gold  and  silver,  126-130 

iron  oxide,  73,  rapid  method,  75 

lead,     fire    assay,     126,     gravi- 
metric, 93 

manganese,  96 

nickel,  as  in  ores,  103 

potassium,  sodium,  lithium,  109 

potassium,      sodium,      sintering 
method,  111 

selenium  and  tellurium,  author's 
method,  111 

selenium  and  tellurium,  Keller's 
method,  112 

silica,    western    method,    71 
eastern  method,  71 

silica,  reverberatory  slags,  72 
silver  slags,  162 

sulphur,  79 

special  solvents,  71 

tin,    separation,    88,   volumetric 
as  in  ore,  114 

titanium,  115 

typolite,  Mansfeld  slags,  66 

zinc,  117 
Sodium,  ores  and  furnace  products,  108 

indirect  separation,   calculation, 
110 

sintering  method,  111 
Sodium  —  arsenite,     titrating     solu- 
tion, 48 

chloride,  silver  precipitant,  48 

citrate,  reagent,  48 

hydroxide,  normal  solution,  re- 
agent, 48 

hypophosphite,    in    arsenic    dis- 
tillation, 202 

phosphate  and  sulphide,  49 

thiosulphate  (hyposulphite),  48 
Solenoid,  or  rotary  device,  description 

11,  use,  189 

Specific  gravity,  compared  with  "den- 
sity," 37 


INDEX 


291 


Spelter,  commercial  zinc: 

classification  of  grades,  253 
cadmium  as  sulphide  and  "Sul- 
phate, including  copper,  256 
cadmium,  electrolysis,  257 
cadmium,  separation  by  trichlor- 

acetic  acid,  258 
iron,  255 

lead,  "acid  method,"  254 
lead,  electrolysis,  255 
sampling,  slabs,  34 
Standard  solutions,  quality  of  chemi- 
cals, 40 

specifications  for  copper,  277 
weights,   12,  use  in   electrolytic 

assay,  185 
Stannous  chloride,  reducing  solution, 

49 

Starch,  indicator  for  hydrogen  sul- 
phide, 50 

indicator  for  arsenic  titration,  51 
Sulphocyanates  —  see  thiocyanates 
Sulphur  determination: 

brass,  bronze,  ornickel  alloys,  246 
copper  metal,  224 
dioxide,  preparation,  39 
iodine  solution  for  titration,  43 
mattes,  and  ores,  raw  and  cal- 
cined, 79 

ores  with  barium  sulphate,  80 
ores,  containing  lead  or  zinc,  80 
pyrites,  special  eastern  methods, 

81 

silver  slimes,  163 
Sulphydrate  of  ammonium,  reagent,  41 


Table  of  chemical  factors,  279 
Tailings  from   stamp  mills,   copper, 

iodide  titration,  51 
copper,  cyanide,  53 
colorimetric,  western  assay,  56 
colorimetric,  eastern  method,  57 
colorimetric,  Mansfeld  shales,  58 
electrolysis,  59 
sampling,  20 

Thiocyanate  of  ammonium,  standard 
solution,  41 


Thiocyanate  of  potassium,  solution, 

47 
Tin  determination,  brass  (with  lead), 

small  amounts,  237 
ordinary  bronze,  242,  phospho- 

bronze,  243 

crude  copper  (with  As,  Sb),  194 
crude  copper,  special  electroly- 
sis, 199 

refined  copper,  accurate  analy- 
sis, 212 
refined    scrap    copper^    accurate 

method,  232 

ores,  electrolytic,  88,  special  titra- 
tion, 114 
Titanium,  standard  solution,  50 

ores  and  slags,  gravimetric,  115 
ores  and  slags,  colorimetric,  116 
copper,  modify  methods,  116 
Tellurium,     estimation     in     copper, 

author's  method,  205 
copper,  Keller's  method,  233 
ores  and  slags,  111-112 
Typolite  ores  and  slags,  copper  assay, 

66 
magnetic  separations,  67 

W 

Water,  estimation  (moisture)  in  clays, 

121 

coal,  loss  in  shipments,  30 
coal,  determination,  31 
Water,    estimation,    converter    and 

blister  copper,  29 
native  copper  concentrates,  140 
ores,  23 

silver  (anode)  slimes,  160 
tailings  from  mills,  20 
Weights,  Atomic  for  1916,  279 

standard,  12,  use  in  electrolytic 

assay,  189 

"assay  ton,"   system  definition 
and  explanation,  125 


Zinc  chloride,  distilling  solution,  50 
Zinc,    estimation    in,    alloys,    brass, 
bronze,  247 


292  INDEX 

Zinc,  nickel  alloys,  monel  metal,  etc.,  Zinc,  cadmium  by  trichloracetic,  258 

248  iron,  255 

alternative  titration  of  Breyer,  lead,  "acid  method,"  254 

249  lead,  electrolysis,  255 
copper    metal,    with    separation  sampling  of  slabs,  34 

from  cobalt  and  nickel,  218  Zinc,    in   ores   and   mattes,   western 

from  cadmium  standard  separa-  assay,  117 

tion,  119  exact  method  (adapted  to  small 

Zinc,  or  commercial  spelter,  classifica-  amounts),  118 

tion,  253  Mansfeld  ores  and  slags,  120 

cadmium,  gravimetric,  with  cop-  furnace   slags,   western  method, 

per,  256  117,  refractories,  123 

cadmium,  electrolytic,  257  separation  from  cadmium,  119 


THE-PLIMPTON-PRESS 
NORWOOD -MASS -U-S -A 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 
BERKELEY 

Return  to  desk  from  which  borrowed. 
This  book  is  DUE  on  the  last  date  stamped  below. 


QCT  1 3  1948 
JUL23195S 


LD  21-100m-9,'47(A5702sl6)476 


J 


32732 


344726 

H, 


, 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


